Conversion Factors

In their simplest form, conversion factors express an equality. They let us relate things that measure the same physical property, but do so using different scales or different units of measure. For example, miles, feet, inches, meters, millimeters all represent the physical property of distance. Each of them uses a different "measuring stick" or scale. Because they are measuring the same physical property, it's possible to equate them, or set them equal to each other. All scales measuring the same physical property can be thought of as belonging to a class of measurement. Common classes of measurement include : distance,   weight, volume, temperature, and time.

Arithmetically, conversion factors can be expressed either as an equality or as a ratio. For example, 12 inches = 1 foot. We make this equality a ratio by setting it equal to 1 as demonstrated below :

 

 

Divide both sides by 1 hr :

 

 

 

Then cancel :

 

 

Because this ratio is set equal to 1, whenever we multiply by the ratio or the conversion factor , we are really just multiplying by 1 - it just doesn't look like it.

Most conversion factors are simple ratios. There are a few that are not. One unit of weight, Grain - thankfully not commonly used anymore - has some goofy conversions because there are several accepted standards. It's actual value is 0.065 grams so it often requires rounding when translating into standard metric units. If you're in Nursing School, use whatever method your instructor has presented. If you're in practice, you're institution's pharmacy will have adopted one or the other of the standards - use their conversion table.

Temperature is another conversion that requires more than a simple ratio. It  requires a scalar in addition to the ratio. See the Temperature page for more info about this .....

 

©1997-2002 Dale Sampson, RN