# Conversion of units

The term "conversion of units" refers to changing an amount of a measurement unit into another unit. There are many different systems of units, so some conversions can be very complex. Most conversions involve a conversion factor (named "m"), and a shift amount (such as "b"), to change from a unit x into a unit y by the general equation: y = m • x + b. That type of conversion is known as a linear transform or a mathematical translation.

A conversion factor is a ratio that lets you convert a measured quantity to a different unit of measure without changing the amount. When a conversion factor is multiplied by the item you are converting, it cancels out the units you do not want and leaves those that you do.[1] Because the top and bottom of conversion factors are the same, conversion factors always equal 1. For example, a conversion factor of (1 day)/(24 hours) equals 1, because 1 day = 24 hours.

One of the most common conversions is to change meters (or "metres") into feet, by multiplying the amount in meters by about 3.28 feet per meter (ft/m):

• Convert 10 meters: 10 meters * 3.28 ft/m = 32.8 feet.

Typically, conversion amounts are rounded to the same precision as the original input amount, such as 10 meters being 33 feet (when 32.8 feet is rounded to 2 digits as "33").

## References

1. Holzner, Steven (2010). Physics Essentials For Dummies. Wiley Publishing. p. 11. .