Lesson 1
Understanding Percentages

You see expressions of percentages scattered about in you everyday life as well as at your work as a nurse or other health professional. For instance, "Street crime has increased by 12%", or "Bring a 0.9% saline solution." Just from everyday living and occupational experience, most of us have a fairly good grasp of the meaning of percentages. But that isn't enough for a health professional--we must also be able to work with percentages on a day-to-day basis and create our own statements of amounts, changes in amounts, and percentages.

What does percent mean?  One clue is the fact that centum is the Latin word for hundred. So when we say "20 percent," we mean 20 per 100, or 20 out of a hundred.

How much is 25 cents? There's that word again—centum. Twenty-five cents is 25 parts of a hundred cents (a hundred cents is, of course, equal to one dollar).

Values expressed as a percentage are being expressed in "parts  per hundred."


Topic 1
Notation for Percents

Percents (parts per 100) are most  often marked with a  percent sign  %.

For example, if 40 out of a hundred cars are colored white, you can say that 40 percent (written as 40%) of cars are painted white.

Examples

6% = six out of a hundred
87% = 87 out of a hundred

fig0501_01.jpg (102794 bytes)

Values that are expressed in percent are labeled with the percent sign, %.

Here are a few everyday examples of  expressing parts-per-hundred with the percent sign:

"Percent solution" is one of the most common expressions of percentage in health and medicine.

Examples:

Express the following amounts as a percentage

1.  30 items out of 100

Ans: 30%

2. 85 items out of 100

Ans: 85%

3.  Two items out of a hundred.

Ans: 2%

 


Percents can also be expressed as fractions -- a percentage value placed over 100.

For example, 12% can  be  expressed as 12/100

30 items out of 100 can be expressed as the ratio, 30/100
85 items out of 100 can be expressed as the ratio, 85/100
Two items out of a hundred can be expressed as the ratio, 2/100
92 parts per hundred can be shown  as 92/100

So, writing a percentage as a ratio (fraction) is a simple matter of showing the number of  items over 100

Procedure

Any percentage  value can be rewritten as a ratio by placing that value over 100

 

Percents can be expresses in decimal form -- a percentage value times 0.01.

For example, 12% can  be  expressed as 12 x 0.01

 

Exercises

Percent Notation

These examples help you master the  three basic forms of notation for percentages.

 

Adjusting Fraction and Decimal Values to % Notation

Most arithmetic operations with percentages are best done using the fraction or decimal forms. Generally speaking, the procedure goes like this:

  1. Convert the % notation to fraction or decimal form
  2. Complete the desired math operations using the fraction or decimal forms
  3. Rewrite the results with % notation
Note

It isn't unusual to display values in one form of notation, but do some math with them in a different form ... and then convert the results back to the customary display notation.

Exercises

Percent Notation

Use these Examples & Exercises to check your understanding  and build your confidence when converting fraction and decimal  notation back to % notation. 

But what if need to  rewrite a fraction with % notation, but the denominator isn't 100? Simply this: Adjust the fraction so that the denominator is 100.

Example 

Problem: Rewrite 15/50 with % notation.

Solution: Multiply both the numerator and denominator by a value that forces the denominator to 100. That value would be 2 in this example:

15 x 2 = 30 =30
50 2 100

15/50 = 30%

Important

It is necessary to multiply the numerator and denominator by the same exact value. This leaves the actual value of the ratio intact.

Exercises

Fraction to % Notation

Use these Examples & Exercises to check your understanding  of how to convert any fraction to the equivalent % notation.


Topic 2
Expanding the Scope of Percent Notation

There is more to the percent number line that integers between 0 and 100.  Here is  what you will be studying in this section:

Percents that have fraction/decimal parts, such as:

56%, %, 37.8%, 3.625%

Percents that are greater than 100,  such as:

 110%, 200%, 102.4%

Percents  with Fraction or Decimal Parts

Sometimes you will find percents that include fractions and decimal values. Financial reports and mortgage rates, for instance, sometimes include percentages written as 6 % or 12.3 %. There is nothing tricky about these fractional parts of a percent. They are simply parts of one-hundred percent.

You will also find percentages that are less than 1. Examples are 0.1%, 0.125%, and so on. These are nothing more than expressions of small percentages—amounts that are less than 1 out of 100.

Recall

To rewrite a percent to decimal:

Drop the % sign and multiply by 0.01

Examples

Rewrite 12 % as a decimal value:     12 x 0.01 = 12.5 x 0.01 = 0.125

Rewrite % as a decimal value:         12 x 0.01 = 12.5 x 0.01 = 0.125

Rewrite 44.25% as a decimal value       44.25 x 0.01 = 0.4425

Exercises

Percent to Decimal

Use these Examples & Exercises to check your understanding  of how to rewrite percents with fraction parts to decimal.

 

Of course, you should also be able to rewrite any fraction or decimal value to percent.

Recall

To rewrite a decimal  or fraction to percent:

Multiply by 100 and attach the % sign.

Examples

Rewrite 0.0625 as a percent:           0.0625 x 100 = 6.25% or 6%

Rewrite 0.005 as a percent:             0.005  x 100 = 0.5% or %

Rewrite 0.00021 as a percent:           0.0002 x 100 = 0.021%

Rewrite 1/8 as a percent:                  1/8 x 100 = 100/8 = 12.5%

Exercises

Decimal to Percent

Use these Examples & Exercises to check your understanding  of how to rewrite any decimal/fraction to percent.

 

 

 

 

 

 

 

 

 

 

 

Rewriting Percents as Decimal Values

Procedure

To rewrite a percent to decimal:

Drop the % sign and multiply by 0.01

Examples

Rewrite 12 % as a decimal value:     12 x 0.01 = 12.5 x 0.01 = 0.125

Rewrite % as a decimal value:         12 x 0.01 = 12.5 x 0.01 = 0.125

Rewrite 44.25% as a decimal value       44.25 x 0.01 = 0.4425

Exercises

Percent to Decimal

Use these Examples & Exercises to check your understanding  of how to rewrite percents with fraction parts to decimal.

 

 

 

 

 

Decimal to Percent

Of course, you should also be able to rewrite any fraction or decimal value to percent.

Procedure

To rewrite a decimal  or fraction to percent:

Multiply by 100 and attach the % sign.

Examples

Rewrite 0.0625 as a percent:           0.0625 x 100 = 6.25% or 6%

Rewrite 0.005 as a percent:             0.005  x 100 = 0.5% or %

Rewrite 0.00021 as a percent:           0.0002 x 100 = 0.021%

Rewrite 1/8 as a percent:                  1/8 x 100 = 100/8 = 12.5%

Exercises

Decimal to Percent

Use these Examples & Exercises to check your understanding  of how to rewrite any decimal/fraction to percent.

Percents Less than 1

 

 

 

 

 

 

 

 

More Examples

Express the following amounts as a percentage

1.  30 items out of 100

Ans: 30%

2. 85 items out of 100

Ans: 85%

3.  Two items out of a hundred.

Ans: 2%

 

 


Topic 2
Fractions, Decimals, and Percents

Percents indicate the amount per 100. So any percentage can be rewritten as a fraction that has 100 as its denominator:

percent =

number or amount
100
Procedure

To convert a percent to a fraction, remove the % sign and divide by 100.

Examples

1. Rewrite 57% as a fraction.

Place the 57 over 100: 7% = 

57
100

2. Rewrite 40% as a fraction

Place the 40 over 100: 40% = 

40
100
Reduce the fraction: 40

, = 

2
100 5

3. Rewrite 61% as a fraction.

This procedure requires an extra step and the understanding that dividing any number by 100 is the same as multiplying it by 1/100.

Convert 61 to an improper fraction:  61

63
2
Divide by 100 (multiply by 1/100): 63

x

1

 =

63
2 100 200

4. Rewrite 110% as a fraction.

Place the 110 over 100:  110

 

100
Reduce the fraction: 110

=

11
1000 10
Rewrite the improper fraction as a mixed number: 11

= 1

1
10 10

Exercises

Rewrite percents as fractions

 


Now let's turn around the operation and rewrite a fraction as a percent.

The basic idea is to convert the two terms of the fraction such that the denominator is equal to 100. For example, rewrite 6/10 as a percent. First you multiply the numerator and denominator by 10. This gives you the necessary value of 100 in the denominator. Finally, remove the denominator and attach the % sign to the remaining value (what had been the numerator).

6

=

6 x 10 = 60
10 10 10 100
  60

, = 60% 

100
Procedure

To convert a fraction to percent, adjust the faction so the denominator is 100, then add the percent sign.

Examples

1. Rewrite 1

 as a percent.

4

Multiply the numerator and denominator by a value that forces the denominator to 100:

1

x

25 = 25
4 25 100
Rewrite 25

 as a percent.

100
  25

, = 25% 

100

 

Exercises

Rewrite fractions as percents

 


Converting between decimal values and percents is much simpler than conversions with fractions.l

Procedures

To convert a percent to a decimal value, drop the % sign and divide by 100.

To convert a decimal value to percent, multiply by 100 and attach the % sign.

Examples

1. Rewrite 30% as a decimal value

Drop the percent sign: 30%   30

Divide by 100:  30 100 = 0.30

30% = 0.3

2. Rewrite % as a decimal value

Drop the percent sign: %  

In this example: rewrite the fraction as a decimal value: = 0.5

Divide by 100:  0.5 100 = 0.005

% = 0/005

3. Rewrite 0.65 as a percent

Multiply by 100:  0.65 x 100 = 65

Attach the percent sign: 65%

4. Rewrite 0.001 as a percent

Multiply by 100:  0.001 x 100 = 0.1

Attach the percent sign:0.1%

 

Exercises

Rewrite fractions as decimals and decimals as fractions

 

 

 

 

40% can be rewritten as 40/100, but such fractions ought to be reduced. So:

40% = 40/100 = 2/5.

 

Examples

 

 

 

You have seen how a given percent can be rewritten as a fraction. It is sometimes necessary to turn that process around and convert a given fractional amount to a percentage. Here is an easy example:

 

11/100 = 11%

This was an easy example because the denominator was already 100.  Now let's work with a fraction that does not have 100 as a denominator. The procedure, in this case, requires you to convert the fraction so that it DOES have a denominator of 100. Then simply rewrite in as a percent. See the following example.

Example

 

P

 

 

 


Topic 3
Working with Percents

There are three terms common to all percentage problems:

In this expression, 5% of 40 = 2

5% is the percentage (P)

40 is the base (b)

2 is the amount of difference (a)

Percentage problems generally fall into three categories:

1. Find percentage of change, given the base and amount of change.

Example: What number is 6% of 50?

2. Find the amount of change when the percentage and base are known.

Example: 20 is what percent of 60?

3. Find the base when the percentage and amount of change are known.

The number 5 is 25% of what number?

Percent of Change

Procedure

To find the percent of change:

Percent of change =

Amount of increase or decrease

x 100

Original amount

In words:

You can determine the percent of change this way:

  1. Divide the amount of increase or decrease by the original amount.

  2. Multiply the result by 100 and attach the percent sign %

 

 

 

 

 

Find the percentage of change when an original amount and new amount are  known

 

A typical verbal problem of this type goes something like this: A certain item in the store normally sells for $60. It is now on sale with a 15% discount. What is the amount of discount? What is the sale price?

The amount of discount is found by calculating 15% of the normal selling price:

Amount of discount is 15% of $60:  0.15 x $60 = $9

The sale price is found by subtracting the amount of discount from the normal selling price:

Sale price = $60 - $9 = $51

A variation of the same kind of problem concerns an independent Web designer who finds she has to increase her rate by 12%. If the current rate is $80 per hour, how much will the hourly rate increase? What is the new hourly rate?

The amount of increase is found by calculating 12% of the current rate.

Amount of increase is 12% of $80:  0.12 x $80 = $9.60

The new rate is then found by adding the amount of increase to the current hourly rate:

New rate = $80 + $9.60 = $89.60

 

 

 

 

Over a period of time, the amount of liquid in a vial drops from 120ml to 50ml. What is the percent of decrease?

The amount of decrease is found by subtracting the lower amount from the original:

Amount of decrease = 120ml - 50ml = 70ml

The percent of decrease is found by taking

The percent of decrease is 70/120 x 100 = 58.3%

 

, what is the new rate?

The amount of increase

 

Exercises

A certain amount is what percent of another amount?

 

 

 

 


Topic 4
Percent of Increase or Decrease

The percent of change (increase or decreases) is an indication of how much a quantity changes.

 

Definition

Percent Change =

Amount of Change  x 100%  
Original Amount  

where the Amount of Change is positive when the amount increases, and negative when the amount is decreasing.

Examples

1. An original amount of 25 units undergoes an increase of 2 units. Determine the percent of change.

Percent Change =

2  x 100% = 8%  
25  

2. A vial containing 500 units of a liquid is reduced by 100 units. Determine the percent of change.

Percent Change =

-100  x 100% = -20%  
500  

3. An item in a store is marked down 14%. Determine the sale price if the item normally sells for $45.00.

 

 

Percent Change =

1  x 100%  
25  

 

Example

 

0402

Lesson 2
Understanding Ratio and Proportion

 

 

 

 

0403

Lesson 3
Introduction to Measurement Standards

 

 

The Metric System of Measurement

Linear Measurements

Linear measurements are measurements of distance. (Linear = Line-like).

The main unit of distance in the metric system is the meter. Think of 1meter as being the distance you would normally find between the center of a doorknob and the bottom of the door, or the floor. All the other labels for distances in the metric system are based on that one particular distance.  Here are some multiples you should know:
 
1 kilometer = 1000 meters 1 km = 1000 m
1 m = 0.001 km
There are a thousand meters in one kilometer. The kilometer is used much like the mile in the US.
1 centimeter = 1/100th of a meter 1 cm = 0.1 m
1 m = 100 cm
There are a hundred centimeters in a meter. The centimeter is used much like the inch in the US.
1 millimeter = 1/1000th of a meter 1 mm = 0.001 m
1 m = 1000 mm
There are a thousand millimeters in a meter (or ten of them in a centimeter).

The standard distance from a doorknob to the floor is approximately 1 meter.

Volume Measurements

In medical practice, volume measurements refer specifically to liquid volume. And in the metric system, the basic unit of liquid volume is the liter. A  standard wine bottle holds 3/4 of a liter. In the US system of measurement, a liter is essentially the same as a quart.

A subdivision of the liter is the milliliter:

1 liter = 1000 milliliters 1 L = 1000 ml There are 5 ml in one teaspoon

You will also see occasional references to the cubic centimeter (cc). The 1 cc is exactly equal to 1 ml.

NOTE

You can use milliliters and cubic centimeters interchangeably. They are simply two different labels for the same amount.

A standard wine bottle holds 3/4 of a liter.

Mass Measurements

The terms mass and weight are often used interchangeably. Technically speaking, they mean different things; however, only physicists and engineers will obsess over the differences.

The basic unit of mass in the metric system is the gram (gm). A standard-size metal paperclip weighs close to 1 gm.

1 kilogram = 1000 grams 1 kg = 1000 g
1 g = 0.001 kg
There are a thousand grams in one kilogram. Units of kilograms are used in much the same way as US pounds (although there is almost a 2:1 difference in their actual masses).
1 milligram = 1/1000th of a gram 1 mg = 0.001 g
1 gm = 1000 mg
Most drugs are specified in terms of milligrams.
1 microgram = 1/1000 of a milligram 1 mcg = 0.001 mg
1 mg = 1000 mcg
1 gm = 1,000,000 mcg
You will often see microgram written as especially in science and technology.

A ripe pineapple weighs about one kilogram

 

The US Standard System of Measurement

The US Standard system of measurement is built around units of feet, fluid ounces, and pounds.

US Linear Measurements

 
1 foot = 12 inches 1 ft = 12 in  
     
     

 

 

US Volume Measurements

 

The units of volume in the US system are:
  • fluid ounce fl. oz
  • pint pt
  • quart qt
  • gallon gal
1 pint = 16 fluid ounces 1 pt = 16 fl. oz
1 fl. oz = 1/16 pt
You will find that fluid ounces (fl. oz) is the most common unit of US volume measurement in medical work.
1 quart = 2 pints 1 qt = 2 pt
1 pt = 1/2 qt
 
1 gallon = 4 quarts 1 gal = 4 qt
1 qt = 1/4 gal
 

 

 

 

US Weight Measurements

 
1 lb = 16 ounces    
     
     

 

 

The Household System of Measurement

The household system of measurement includes all the common (and many not-so-common) measurements found throughout traditional kitchen recipe books. Only three household measures have any significance for health care:
 

teaspoon tsp

tablespoon tbs

cup c

drop gtt

 

     
  3 tsp = 1 tbs  
     

 

 

The Apothecary System of Measurement

Like the household system of measurement, the apothecary system has a relatively large number of units. The relationships between the units are often complicated and curious. Fortunately, there is only apothecary label still in common use for general health care:  the grain.

grain gr

 

0404

Lesson 4-4
Working with Dimensional Analysis
The term dimensional analysis sounds more like something you might find in rocket science than medicine. However, dimensional analysis is actually a simple, but powerful idea. It is simple because it always takes the same form:  a series of two or more ratios that are multiplied together. It is powerful because it virtually eliminates the need for recalling large numbers of measurement conversions and formulas.  Master the basic idea of dimensional analysis, and you no longer have to ask, " Do I multiply or divide to make this conversion or calculate this dosage?"

Dimensional analysis is NOT rocket science.

Relative Amounts and Ratios

Recall that a ratio expresses the relative value of two amounts. "Two out of three, " for example,  can be expressed as the ratio 2/3. "One in a hundred" can be expressed as 1/100.

Now consider the fact that there are 16 fl. oz in a pint. That can also be expressed as a ratio:  . That is saying "Sixteen fluid ounces per one pint." It's a ratio that happens to include labels as well as numerical values.

You know that there are 100 cm in a meter. This can be expressed in two ways:

  says there are 100 centimeters in a meter.

says there is 1 meter per 100 centimeters.

Both are correct. Both say the same thing. The ratios are equal.

The success of dimensional analysis depends your knowing:
  • A ratio and its inverse (flipped-over version) are equal
  • Which of the two ratios are to be used solving a given problem.

Examples 1:

Express each of the following conversions as two ratios.

Known Conversion Ratios
There are 12 inches in one foot
12 in
1 ft
1 ft
12 in
There are 1000 ml in a L
1000 ml
1 L
1 L
1000 ml
16 oz = 1 lb
16 oz
1 lb
1 lb
16 oz
You can substitute 3 teaspoons of medicine for one tablespoon.
3 tsp
1 tbs
1 tbs
3 tsp

 

You know it is not unusual to have medications mixed with sterile water. The concentration of the medication can then be expressed as mg of medication per ml of fluid. So if there is 10 mg of medication in 100 ml mixture, the concentration can be expressed as:

Ten milligrams per milliliter
or
One hundred milliliters per milligram
 

Expressing Relative Amounts as a Pair of Ratios

Work with this drill routine until you can consistently make the conversions correctly.

Click the Answer button to see the correct answer to the question.
Click the Next button to see the next question.

Setting Up Ratios to "Cancel" Labels

When you first studied rations and proportions, you found that you can "cancel" equal terms in order to simplify the multiplication of fractions or ratios.

Example

Given:

5

x

3  
8 5

Cancel "crosswise" terms that are equal

5 x 3 = 1 x 3
8 5 8 1

Complete the multiplication

1 x 3 = 3
8 1 8

For the purposes of dimensional analysis, you can also "cancel" labels:

 

 

 

Explanation

In the first step, you are simply setting up a product of two ratios you should know:  there are 100 mm in 1 cm, and there are 10 cm in 1 m.

100 mm

x

10 cm  
1 cm 1 m

In the second step, notice that cm appears in the denominator of one term and in the numerator of the other term. This means you can "cancel" the cm labels not the numerical values, but the labels, themselves.

100 mm

x

10 cm  
1 cm 1 m

The third step simply shows the product of the two ratios, having cancelled out the common labels (cm, in this example)

100 mm

x

10  
1 1 m

And finally, you complete the multiplication of the numerical terms, sliding the remaining labels over into the final ratio.

100 mm x 10 = 1000 mm
1 1 m 1 m

The final result says that there are 1000 mm in one meter. And of course that is  true.

Example 2:

Use a product of ratios (dimensional analysis) to convert 575 milligrams to grams.

The given amount is 575 mg. Expressing this as a ratio:

You should know that the conversion ratio for milligrams and grams is

Set up those two ratios for multiplication:

Strike out labels that can be cancelled:

Complete the multiplication:

Answer: 575 mg is equal to 0.575 g

 

"Cancelling Labels" and Completing the Multipication

The ratios have been set up for you in this drill. Your job is to complete the task by cancelling labels are appropriate and doing the multiplication.

Click the Answer button to see the correct answer to the question.
Click the Next button to see the next question.

 

Important

The whole trick to dimensional analysis is to set up the ratios in such a way that all the labels you don't  want in the final result are "cancelled." 

Example 3

Convert 1500 mg to grams.

The given ratio is and you want the result to be in grams. So you need a conversion ratio for converting between milligrams and grams.

The conversion ratios you can choose from are and . These ratios are equal. They are both used for converting between units of milligrams and grams. The big question is this: which one do you use in our example for converting 1500 mg to grams?

Let's try the analysis using the conversion ratio, .

The trouble with using this form of the conversion ratio is that none of the labels cancel.  So It must be the wrong choice.

So try the other version, ,and see what happens:

Now the mg labels cancel, leaving the answer in grams.

1500 mg is equal to 1.5 g.

Example 4

Convert 0.2 pounds to ounces.

The given ratio is:

The conversion ratios for pounds and ounces are and

Which one should you use for converting the given ratio to units of ounces?

Try doing the analysis with the first conversion ratio:

You can see that the pound (lb) labels will cancel, leaving on the oz label for the answer. So that is the correct choice:

Try the other conversion ratio, , and you will see that nothing can be cancelled.

Ans: 0.2 lb = 3.2 oz.

 

Choosing Conversion Ratios

Select the ratio that allows you to cancel all unwanted labels, leaving only the label(s) required for the final answer.

Click the Answer button to see the correct answer to the question.
Click the Next button to see the next question.

The Structure of Dimensional Analysis

The most convincing reason for using dimensional analysis is simplicity. Every conversion problem and every dosage calculation look exactly the same way products of ratios. And there are just three basic kinds of ratios:

The Given Ratio is the one that shows the information given by the problem. If you are required to convert 122 inches to feet, for example, the given amount is 126 in, and given ratio is .

The Conversion Ratio is the one that contains the necessary conversion numbers and labels. When converting between inches and feet, the correct conversion ratio is .

The Result Ratio is the product of the given ratio and conversion ratio:  . (The Result Ratio should be simplified to a single term when you have finished the work. In this example,  should be simplified as 10.5 ft).

There can be only one Given Ratio and One Result Ratio, but there can be more than one Conversion Ratio. This happens when there is more than one unit conversion involved in the problem.

Here is an example of a dimensional analysis that uses two conversion ratios to complete the job. Don't panic over the  complicated-looking equation. Just identify the parts and note that each one says something you probably understand rather well. In this example, you convert a speed expressed in meters per second into a speed expressed in kilometers per hour.

Such problems usually get people all anxious about which to multiply or divide my which. Dimensional analysis, however, orders everything.

Example 5

Convert 2000 meters per second into kilometers per hour.

The Given Ratio is

One of the conversion ratios has to deal with seconds and hours: or

The second conversion ratio works with meters and kilometers:  or

The dimensional analysis look like this:

Note how the conversion ratios are selected so that the meters and seconds cancel, leaving just the desired kilometer and hour.

0405

Lesson 4-5
Mastering Length Conversions

 

Length Conversions

 

 

 

Units of Measure for Length
Metric US Standard
millimeter
centimeter
meter
kilometer
mm
cm
m
km
inch
foot
yard
mile
in
ft
yd
mi

 

Most Common Conversion Factors for Length

Metric US Standard System Conversion
1000 m per 1 km

100 cm per 1 m

1000 mm per 1 m

12 in  per 1 ft

3 ft per 1 yd

5280 ft per 1 mi

2.54 cm per 1 in

1.61 km per 1 mi

 

Length Conversion Map

Metric Length Conversions

Metric length conversions are relatively easy because the conversion factors are all multiples of 10.  You don't need the aid of a calculator because all the calculations are simply multiplying or dividing by multiples of 10.

100 mm per 1 cm
or
1 cm per 100 mm
100 cm per 1 m
or
1 m per 100 cm
1000 m per 1 km
or
1 km per 1000 m

 

Example 1: Converting meters to centimeters

Convert 0.12 m to cm.

Given Length:  0.12 m
Conversion Factor: 
100 cm/m
 
Set up the ratios:
Cancel the labels:
Complete the math:
Result: 120 cm  

Example 2: Converting centimeters to meters

Convert 1500 cm to m.

Given Length:  1500 cm
Conversion Factor: 
1 m/100 cm
 
Set up the ratios:
Cancel the labels:
Complete the math:
Result: 1.5 m  

 

 
Emoticon - Brilliant Idea Get the idea? Systematic dimensional analysis (conversion ratios) can save a lot of grief!

You can use the same easily remembered conversion factor 100 cm per 1 m to convert meters to centimeters or vice versa.

You don't have to deal with that old problem of trying to remember whether to multiply or to divide. Simply set up the conversion ratio so it cancels the label for the given amount.

Example 3: Converting meters to kilometers

Convert 16500 m to km

Given Length:  16500 m
Conversion Factor:  1 km/
1000 m
 
Set up the ratios:
Cancel the labels:
Complete the math:
Result: 16.5 km  

Example 4: Converting centimeters to millimeters

Convert 0.175 cm to mm

Given Length:  0.175 cm
Conversion Factor:  100 mm/
1 cm
 
Set up the ratios:
Cancel the labels:
Complete the math:
Result: 17.5 mm  

 

Metric-to-Metric Conversion Drill

Work with this drill routine until you can consistently make the conversions correctly.

Click the Answer button to see the correct answer to the question.
Click the Next button to see the next question.

US Standard Length Conversions

US Standard conversions are a bit more difficult than metric conversions, mainly because the conversion factors are not simple multiples of 10:

So a calculator can be helpful at times for making conversions that include any US Standard lengths.

NOTE

Leave answers in decimal form. All but the US building trades use decimal forms of US Standard lengths. For example, cite 1.25 ft instead of 1 ft 3 in., and 1.5 inches instead of 1 ".

Example 5: Converting Inches to Feet

Convert 44 in to ft.

Given Length:  44 in
Conversion Factor: 
1 ft/12 in
 
Set up the ratios:
Cancel the labels:
Complete the math:
Result: 3.67 ft  

Example 6: Converting Yards to Feet

Convert 1.25 yd in to ft.

Given Length:  1.25 yd
Conversion Factor: 
3 ft/1 yd
 
Set up the ratios:
Cancel the labels:
Complete the math:
Result: 3.75 ft  

US Standard Conversion Drill

Work with this drill routine until you can consistently make the conversions correctly.

Click the Answer button to see the correct answer to the question.
Click the Next button to see the next question.

Converting Between Metric and US Standard Lengths

Here is the only conversion ratio you must be able to recall. You can use dimensional analysis with two conversion factors to work with any other combination of metric and US terms.

Example 7: Converting Centimeters to Inches

Convert 43 centimeters to inches

Given Length:  43 cm
Conversion Factor:  2.54 cm/in
 
Set up the ratios:
Cancel the labels:
Complete the math:
Result: 16.93 in  

Example 8: Converting feet to centimeters

How many centimeters are in 1 foot?

If you don't happen to recall the number of centimeters in a foot, you can use a 2-step conversion: 

  1. Convert feet to inches using the ratio you know:  2.54 cm/ in
  2. Convert that result to feet using another ratio you know: 12 in/ft

Given Length:  1 ft
Conversion Factors:  12 in/ft, 2.54 cm/in
 
Set up the ratios:
Cancel the labels:
Complete the math:
Result: 30.5 cm  

Example 9: Converting miles to kilometers

How many miles are in 4 kilometers?

Make this a special challenge by assuming you do not recall the number of kilometers in one mile. All you can recall is: 2.54 cm/1 in, 12 in/1 mi, and 5280 ft/mi.

Given Length:  4 km
Conversion Factors: 
     1000 m/km, 100 cm/m, 1 in/2.54 cm, 1 ft/12 in, 1 mi/5280 ft
 
Set up the ratios:
Cancel the labels:
Complete the math:
Result: 2.49 mi  

 

Example 10: Converting millimeters to inches

Convert 150 mm to inches.

Given Length:  150 mm
Conversion Factors:  2.54 cm/in, 10 mm/cm
 
Set up Given Length and Conversion Factor 1:
Attach Conversion Factor 2:
Cancel the labels:
Complete the math:
Result: 0.59 in  

Ans: 150 mm is 0.59 in

Metric/US Standard Conversion Drill

Work with this drill routine until you can consistently make the conversions correctly.

Click the Answer button to see the correct answer to the question.
Click the Next button to see the next question.

 

0406

Lesson 4-6
Mastering Volume Conversions

 

Volume is the measure of the amount of space an object or substance occupies. A grain of sand has a minuscule volume compared with the Rock of Gibraltar; nevertheless, the lowly grain of sand has a measurable volume. Solids, liquids, and gasses that are confined to some sort of container, all occupy space and can be measured in terms of their volume.
 

In the healthcare profession--especially when talking about medications--the term volume refers to liquid measurements.

 

Units of Measure for Liquid Volume
Metric US Standard Apothecary
microliter
milliliter
liter
mcm
ml
L
fluid ounce
pint
quart
gallon
fl. oz
pt
qt
gal
grain
gr

 

NOTES:

You will occasionally see liquid volume expressed in units of cubic centimeters (cc). This isn't a cause for concern, however, because 1 cc is the same as 1 ml.

As a health professional, you won't work with microliters (mcm) very often. Science and technology professions prefer the label mL.

The US Standard ounce is properly called a fluid ounce (fl. oz) to distinguish it from the weight/mass version where 16 ounces (oz) equals one pound (lb).

 

Most Common Conversion Factors for Liquid Volume

Metric US Standard System Conversion
1,000,000 mcm per L

1000 ml per L

16 fl.oz per pt

2 pt per  qt

4 qt per gal

1 qt = 0.946 L

Volume Conversion Map

 

Metric Volume Conversions

Metric volume conversions are relatively easy because the conversion factors are all multiples of 10.  In fact, there is only one purely metric volume conversion:  milliliters to liters and vice-versa.

1000 ml per 1 L
or
1 L per 1000 ml

 

Note: The cubic centimeter (cc) measurement is still used today, but you should easily remember that 1 cc is equivalent to 1 ml.

 

Example 1: Converting Milliliters to Liters

Convert 1250 ml to L

Given Volume:  1250 ml
Conversion Factor:  1 L per 1000 ml
 
Set up the ratios:

1250 ml

x

1 L  
1 1000 ml
Cancel the labels:

1250

x

1 L  
1 1000
Complete the math:

1250

x

1 L = 1.25 L
1 1000
Result: 1.25 L  

Example 2: Converting Liters to Milliliters

Convert 0.055 L to ml

0.055 L

x

1000 ml  
1 1 L

0.055

x

1000 ml  
1 1

0.055

x

1000 ml  = 55 ml
1 1

0.055 L = 55 ml

Note

Notice how you don't have to figure out whether your are supposed to multiply or divide. You simply take the proper conversion factor ( 1000 ml per 1 L, in these examples) and arrange it so the unwanted labels cancel out.  In Example 1, you want to get rid of the ml label, so you flip over the conversion ratio so that the ml label is on the bottom. In Example 2, you want to get rid of the L label, so you flip over the same conversion factor so that L labels cancel.

Examples 3: Converting Between Liters and Cubic Centimeters

3-1. Convert 0.15 L to cc.

0.15

x

1000 cc = 150 cc
1 1

3-2  1280 cc = _____ L

1280

x

1 L

= 1.28 L
1 1000

Metric Volume Drill

Work with this drill routine until you can consistently make the conversions correctly.

Click the Answer button to see the correct answer to the question.

Click the Next button to see the next question.

US Volume Conversions

The US Standard volume measurements most commonly encountered in the healthcare professions are:

16 fl.oz per pt
or
1 pt per 16 fl.oz
2 pt per 1 qt
or
1 qt per 2 pt
4 qt per 1 gal
or
1 gal per 4 qt

Example 4: Converting Fluid Ounces to Pints

Convert 18 fl. oz to pt

Given Volume:  18 fl. oz
Conversion Factor:  1 pt per 16 fl. oz
 
Set up the ratios:

18 fl. oz

x

1 pt  
1 16 fl. oz
Cancel the labels:

18

x

1 pt  
1 16
Complete the math:

18 

x

1 pt = 1.13 pt
1 16
Result: 1.13 pt  

Examples 5: Converting US Volume Measurements

5-1. Convert 0.1 pint to units of fluid ounces.

0.1

x

16 fl. oz = 1.6 fl. oz
1 1

5-2. Convert 10 pt to qt.

10

x

1 qt = 5 qt
1 2

5-3. Convert 0.1 gallon to quarts.

0.1

x

4 qt = 0.4 qt
1 1

Sometimes you have to use multiple conversion ratios, rather that looking up conversion factors you haven't memorized.

5-4. Convert 1600 fluid ounces to gallons.

US Standard Volume Drill

Work with this drill routine until you can consistently make the conversions correctly.

Click the Answer button to see the correct answer to the question.
Click the Next button to see the next question.

 

Metric/US Volume Conversions

It is possible to make up all sort of metric-to-US and US-to-metric volume conversions, but there is just one that stands out from the rest: converting between cc (or ml) and fluid ounces. In fact, if you memorize this conversion ratio you will be able to use multiple conversion ratios to work out any other metric/US volume conversion without having to memorize or look up their ratios.

1 fl. oz per 29.6 ml
or
29.6 ml per fl. oz

Note

Recall that 1 cc = 1 ml, so you can also put the ratio this way:

1 fl. oz per 29.6 cc
or
29.6 cc per fl. oz

Example 6: Converting Fluid Ounces to Cubic Centimeters

Convert 3/4 fl. oz to cc

Given Volume:  0.75 fl. oz
Conversion Factor:  29.6 cc per fl. oz
 
Set up the ratios:

0.75 fl. oz

x

29.6 cc  
1 1 fl. oz
Cancel the labels:

0.75

x

29.6 cc  
1 1
Complete the math:

0.75

x

29.6 cc = 22.2 cc
1 1
Result: 22.2 cc  

Examples 7: Converting Between Metric and US Volume Measurements

7-1. 100 ml = _____ fl. oz

100

x

1 fl. oz = 3.4 fl. oz
1 29.6

 

7-2. 1 L = _____ fl. oz

The conversion ratio for liters and fluid ounces is not ordinarily provided on conversion charts. So it is necessary to convert the liter to another unit that is normally associated with fluid ounces ... and that would be ml.  You should know by now that 1 L = 1000 ml, so substitute that ratio:

So instead of trying to work with liters

1

x

1 fl. oz =
1 ???

work with the equivalent number of ml--a conversion ratio that is more commonly known:

1000

x

1 fl. oz = 33.8 fl. oz
1 29.6

Answer: 1 L = 33.8 fl. oz

 

Fluid Ounces and Cubic Centimeter Drill

Work with this drill routine until you can consistently make the conversions correctly.

Click the Answer button to see the correct answer to the question.
Click the Next button to see the next question.

Household  Volume Measurements

The household volume measurements you are likely to encounter as a health worker are cup (c) , teaspoon (tsp or t), and tablespoon (tbs or T). Here are the conversion ratios:
5 ml per 1 tsp
or
1 tsp per 5 m
l
3 tsp per 1 tbs
or
1 tbs per 3 tsp
8 fl. oz per c
or
1 c per 8 fl. oz

Also remember that units of ml and cc are identical.

Examples 8: Converting Household Volume Measurements

8-1.  The instructions on a bottle of cough medicine call for taking 2 tsp every six hours. How much is each dose in ml?

8-2. How many cubic centimeters in one cup?

Recall that 1 fl. oz = 29.6 cc

8-3. 1 tbs = _____ ml

Household Measurements Drill

Work with this drill routine until you can consistently make the conversions correctly.

Click the Answer button to see the correct answer to the question.
Click the Next button to see the next question.

Topic Summary: Volume Conversions

Volume Conversions Drill

Work with this drill routine until you can consistently make the conversions correctly.

Click the Answer button to see the correct answer to the question.
Click the Next button to see the next question.

0407

Lesson 4-7
Mastering Mass/Weight Conversions

 

Metric US Standard Apothecary
microgram
milligram
gram
kilogram
mcg
mg
g
kg
ounce
pound
ton
oz
lb
T
grain
gr

 

Note

The label for micrograms (mcg) is used primarily in medicine and pharmacy. It is written as mg in most technical trades and science professions.

 

 

 

Mass (Weight) Conversion Map

 

 

Metric Mass Conversions

 

 

1000 mcg per 1 mg
or
1 mg per 1000 mcg
1000 mg per 1 g
or
1 g per 1000 mg
1000 g per 1 kg
or
1 kg per 1000 g

Example 1: Converting Micrograms to Milligrams

Convert 3500 micrograms to milligrams.

Given Mass:  3500 mcg
Conversion Factor:  1000 mcg per 1 mg
 
Set up the ratios:
Cancel the labels:
Complete the math:
Result: 3.5 mg  

 

Examples 2: Converting Metric Mass

2-1. Convert 0.02 gm to milligrams.

2-2. Express 5 mg in micrograms.

Volume Conversions Drill

Work with this drill routine until you can consistently make the conversions correctly.

Click the Answer button to see the correct answer to the question.
Click the Next button to see the next question.

 

US Standard Mass (Weight) Conversions

 

16 oz per 1 lb
or
1 lb per 16 oz
2000 lb per 1 T
or
1 T per 2000 lb

Example 3. Converting Pounds to Ounces

Convert 35 oz to pounds

Given Mass:  35 oz
Conversion Factor:  1 lb per 16 oz
 
Set up the ratios:
Cancel the labels:
Complete the math:
Result: 2.19 lb  

Mass Conversions Drill

Work with this drill routine until you can consistently make the conversions correctly.

Click the Answer button to see the correct answer to the question.
Click the Next button to see the next question.

 

 

Mixed-Standard Mass Conversions

1 gr per 60 mg
or
60 mg per 1 gr

Examples x: Converting Grains

 

 

 

How many grains in one ounce?

 

 

 

 

0408

Lesson 4-8
Mastering Time and Rate Conversions

 

 

 

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