Inch in

Symbolin
SystemImperial & US Customary
QuantityLength
Value in SI25.4 mm (exact)
Defined / adopted1959 international yard

About the Inch

The inch is defined as exactly 25.4 millimetres. Britain and the United States agreed this value in the 1959 international yard and pound agreement, which ended small differences between national standards. Earlier the inch was traditionally three barleycorns. Screens, tyres and pipes are still sized in inches worldwide.

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