Length is generally described as the longest dimension of an object. Length is a measure of one dimension, whereas area is a measure of two dimensions and volume is a measure of three dimensions.

Imperial / American measurements

For the imperial system the commonly used units of length are the inch, the foot, the yard, and the mile.

Metric measurements

In the metric system the basic unit of length is the metre and is defined in terms of the speed of light.


An inch (plural: inches; abbreviation or symbol: in or ") is a unit of length in the imperial and United States customary systems of measurement. Traditional standards for the exact length of an inch have varied in the past, but now the imperial or US customary inch is defined to be exactly 25.4 mm. There are 12 inches in a foot and therefore 36 inches in a yard.


The foot (plural: feet) is a unit for measuring length. It is one of the Imperial units and U.S. customary units. The shortest way of writing the unit "foot" is by the abbreviation "ft" (or "ft."), or by an apostrophe ( ' ). One foot contains 12 inches.

1 inch = 0.083 ft