Inch

The inch (symbol: in or <a href="/facts/Prime_(symbol)/3p9EvU5X">″</a>) is a <a href="/facts/Units_of_measurement/pvTpWbmC">unit</a> of <a href="/facts/Length/EwFyAqGH">length</a> in the <a href="/facts/Imperial_units/XBpM6M1W">British Imperial</a> and the <a href="/facts/United_States_customary_units/s76n3Bx4">United States customary</a> <a href="/facts/System_of_measurement/xIsWmFWW">systems of measurement</a>. It is equal to ⁠1/36⁠ <a href="/facts/Yard/ddkwJz1q">yard</a> or ⁠1/12⁠ of a <a href="/facts/Foot_(unit)/XKamEGjV">foot</a>. Derived from the <a href="/facts/Uncia_(unit)/nXdWtaoL">Roman uncia</a> ("twelfth"), the word inch is also sometimes used to translate similar units in other measurement systems, <a href="/facts/Anthropic_units/palbn0UT">usually understood as deriving</a> 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 <a href="/facts/International_yard/awSvK9or">international yard</a> during the 1950s and 1960s the inch has been based on the <a href="/facts/Metric_system/to24H0YK">metric system</a> and defined as exactly 25.4 <a href="/facts/Millimetre/25mdTXpa">mm</a>.

Inch open-in-new

Inch