Inch

Inch
A measuring tape with inches
General information
Unit system	Imperial/US units
Unit of	Length
Symbol	in, ″ (the double prime)[1]
Conversions
1 in in ...	... is equal to ...
Imperial/US units	1/36 yd or 1/12 ft
Metric (SI) units	25.4 mm

The inch (symbol: in or ″) is a unit of length in the British Imperial and the United States customary systems of measurement. It is equal to 1/36 yard or 1/12 of a foot. Derived from the Roman uncia ("twelfth"), the word inch is also sometimes used to translate similar units in other measurement systems, usually understood as deriving from the width of the human thumb.

Standards for the exact length of an inch have varied in the past, but since the adoption of the international yard during the 1950s and 1960s the inch has been based on the metric system and defined as exactly 25.4 mm.