Inch


 * For other meanings, see Inch (disambiguation).

An inch (plural: inches; symbol or abbreviation: in or, sometimes, ″ — U+2033 - a double prime) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary units. Its size can vary from system to system. There are 36 inches in a yard and 12 inches in a foot. A corresponding unit of area is the square inch and a corresponding unit of volume is the cubic inch.

The inch is one of the dominant units of measurement in the United States, and is commonly used in Canada. In the US and commonly in the UK and Canada, personal heights are expressed in feet and inches by people of all ages, and by people over the age of about 40 in Australia. In Australia, Canada and New Zealand, personal heights are shown in metric units on official documents.

International inch
In 1959 the United States and countries of the Commonwealth of Nations defined the length of the international yard to be exactly 0.9144 meters. Consequently, the international inch is defined to be exactly 25.4 millimeters.

The international standard symbol for inch is in (see ISO 31-1, Annex A). In some cases, the inch is denoted by a double prime, which is often approximated by double quotes, and the foot by a prime, which is often approximated by an apostrophe. For example, 6 feet 4 inches is denoted as 6&prime;4&Prime; (or approximated as 6'4").