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 one convert a measured quantity to a different unit of measure without changing the amount. When a conversion factor is multiplied by the item one are converting, it cancels out the units they does not want and leaves those that they do. 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").