can also be called:
Factor label method
How do I change units on a number?
Unit conversions in the geosciences
Introduction to unit conversionsIn the geosciences, we think about how the Earth works on a variety of scales. For example, the San Andreas Fault that runs nearly the length of California's coastline is over 1200 km long.
How do I do a unit conversion?
You can do any unit conversion if you follow a few simple steps. Although there is no single "right" way to do unit conversions, these steps provide one way to learn to do unit conversions. DO NOT SKIP ANY STEPS! Although it may seem tedious, working through unit conversions requires that each of these steps be followed so that you can be sure that you end up with what you want, especially when you are just starting out with learning to do unit conversions.
Below, you can download and print some tables for your use when doing unit conversions:
When you do any unit conversion, you should always know what units you started with and what units you want to end up with. This is key to success at unit conversions.
The StepsThe steps to successfully completing a unit conversion are outlined below. To illustrate the steps, lets use a geologic example: In Southern California, slip on the San Andreas Fault is on the order of 25 km/Myr. How many cm does the San Andreas Fault move in one year?
- Write (copy) out the units that you are given as a fraction.
- Write out the units that you want at the end of the conversion as a fraction:
- Determine appropriate conversion factors. Use tables in your textbook or download one of the tables listed above (for this particular example, you probably only need to know the prefixes for metric system (Acrobat (PDF) 7kB Aug31 11)).
- Evaluate the appropriate arrangement for conversion factors. That is, copy the conversion factor(s) from step 3 into fraction form so that the units end up canceling. Remember that when you multiply fractions (as you will in step 6 below), you can cancel units ONLY when they appear in the numerator of one fraction and the denominator of another.