An inch (in or ") is a unit of length in the US customary system and imperial systems of measurement. It is one of the units of length still commonly used in the US today that is not part of the International System of Units (SI). Other lengths that are still in use that are part of the US customary system include the foot, yard, and mile. The inch is the smallest of these lengths.

1 mile = 1760 yards = 5280 feet = 63360 inches

The definition of an inch has changed over time but is currently based on the metric system, and is defined as 2.54 centimeters (cm).

Inches are often used alongside feet to specify a person's height in the US. For example, since there are 12 inches in 1 foot, someone who is 63 inches tall is 5 ft 3 in tall. This can also be written as 5'3". This is most common in the US, as many other countries measure height in centimeters, and would convey the same height as 160.02 cm.

Like the US survey foot the US survey inch is also still in use for survey purposes, since there was already a lot of existing data prior to the redefinition of the inch in 1959 based on the metric system, so the US chose to continue using the survey foot for surveying purposes.

Did you know?

At one time in English history, an inch was defined as the width of a man's thumb. Today an inch can be defined as 2.54 centimeters (cm), which is about the length of a child's thumb from the tip to the first joint.

See also U.S. customary units.