Inch (in)
Definition
The inch (symbol in, plural inches) is an imperial and US customary unit of length equal to exactly 25.4 millimeters, or 1/12 of a foot. It is widely used for screen sizes, hardware dimensions, clothing sizes, and rainfall in the United States.
History
The inch traces to the Old English ynce, derived from the Latin uncia meaning one-twelfth. King David I of Scotland and later King Edward II of England linked it to barleycorns: three barleycorns laid end to end made one inch.
Different inch lengths persisted in different countries until the 1959 international yard and pound agreement defined the inch as exactly 25.4 millimeters. This figure was already in use under the British Standards Institution from 1930 and was formally adopted by the U.S. National Bureau of Standards (now NIST) in 1933 for industrial work.
Standard reference
Defined under the 1959 international yard and pound agreement as 25.4 mm exactly. NIST Special Publication 811 confirms this value as the only inch in U.S. legal use.
Common conversions
| 1 in | = 0.0254 m |
|---|---|
| = 2.54 cm | |
| = 25.4 mm | |
| = 0.0833333 ft |