The inch is an "English" or "Imperial" unit of length, being the 1/12 of a foot, and about 2.54 centimeters. This inch, along with the feet, bushels, and pounds, is mostly used in the United States of America, it being one of the few industrial nations of the world that still clings to it.

The Chinese inch ("tswen") is approximately 3.03 centimeters, to my best estimation, but it is infrequently used in most areas in favor of the metric system.

Curiously, the inch is exactly 2.54 cm. The story goes that Henry Ford was frustrated at the lack of standardization of parts measurements and things; the US at that time used various different inches, while the cm was fixed. So Ford asked Swedish inventor Carl Edward Johansson to make some end-gauge for Ford's factories. Johansson was happy to, so while Congress mucked around trying to come up with a standard, he picked the handy 2.54 cm to an inch that we know today and delivered the blocks. The 2.54 conversion allowed a switch from metric to imperial threads in a lathe by using two wheels with 100 and 127 cogs on them. 2.5 cm would have worked too, but it was too disparate from the majority of inches. 2.54 was just close enough.

Inch (?), n. [Gael. inis.]

An island; -- often used in the names of small islands off the coast of Scotland, as in Inchcolm, Inchkeith, etc.

[Scot.]

Inch, n. [OE. inche, unche, AS. ynce, L. uncia the twelfth part, inch, ounce. See Ounce a weight.]

1.

A measure of length, the twelfth part of a foot, commonly subdivided into halves, quarters, eights, sixteenths, etc., as among mechanics. It was also formerly divided into twelve parts, called lines, and originally into three parts, called barleycorns, its length supposed to have been determined from three grains of barley placed end to end lengthwise. It is also sometimes called a prime (�xb7;), composed of twelve seconds (�xb7;�xb7;), as in the duodecimal system of arithmetic.

<-- �xb7; is the same symbol as the light accent, or the "minutes" of an arc. The "seconds" synbol should actually have the two strokes closer than in repeated "minutes". Here, �xb7;�xb7; will be interpreted as "seconds" -->

12 seconds (�xb7;�xb7;) make 1 inch or prime. 12 inches or primes (�xb7;) make 1 foot. B. Greenleaf.

⇒ The meter, the accepted scientific standard of length, equals 39.37 inches; the inch is equal to 2.54 centimeters. See Metric system, and Meter.

2.

A small distance or degree, whether or time space; hence, a critical moment.

Beldame, I think we watched you at an inch. Shak.

By inches, by slow degrees, gradually. -- Inch of candle. See under Candle. -- Inches of pressure, usually, the pressure indicated by so many inches of a mercury column, as on a steam gauge. -- Inch of water. See under Water. -- Miner's inch, Hydraulic Mining, a unit for the measurement of water. See Inch of water, under Water.

Inch (?), v. t. [imp. & p. p. Inched (?); p. pr. & vb. n. Inching.]

1.

To drive by inches, or small degrees.

[R.]

He gets too far into the soldier's grace And inches out my master. Dryden.

2.

To deal out by inches; to give sparingly.

[R.]

Inch, v. i.

To advance or retire by inches or small degrees; to move slowly.

With slow paces measures back the field, And inches to the walls. Dryden.

Inch, a.

Measurement an inch in any dimension, whether length, breadth, or thickness; -- used in composition; as, a two-inch cable; a four-inch plank.

Inch stuff, boards, etc., sawed one inch thick.