This converter makes instant conversions between common length units, including millimeters (mm), centimeters (cm), meters (m), kilometers (km), inches (in), feet (ft), yards (yd), and miles (mi). To use this converter, please select the desired units and provide a value to convert. The converter will make conversions as the value is being typed in.
Popular length conversions
Length as a measurement
Length is a measurement of distance. There are many different units of length within various systems of measurement. The most commonly used include lengths in the International System of Units (SI) such as meters, kilometers, centimeters, millimeters, and more, depending on the magnitude of the distance being measured. In SI, the base unit of length is the meter. Other measurements of length in SI are relative to the meter and indicated with a metric prefix such as kilo-, centi-, milli- etc. Each prefix denotes some power of 10 by which the unit differs from the meter. For example, a centimeter is 1/100 m while a kilometer is 1,000 m.
The US customary system of units and imperial system are two other commonly used systems of measurement. Unlike SI, in these systems, the various measurements of distance are not relative to some base unit. Each unit is defined in relation to each other, but knowing the conversions between each unit is similar to converting between different systems of measurement – the conversion factor simply requires rote memorization. For example, below are a few commonly used measurements of length in the US customary system stated in terms of inches:
- 1 foot = 12 inches
- 1 yard = 3 feet = 36 inches
- 1 mile = 1760 yards = 5,280 feet = 633,360 inches
The above conversions provide an example of why there are so many different units of length even within the same system of measurement; it would not be efficient to measure large distances in terms of inches rather than a larger unit of length.