inch

The inch is a unit of length in the imperial and United States customary systems. It is defined as 1/12 of a foot and is equal to 2.54 centimeters in metric terms. The inch is commonly abbreviated as in and is used in everyday and technical measurement.

Officially, the international inch has been defined as exactly 25.4 millimeters since 1959, a standard adopted by the United States, the United Kingdom, and other nations that use customary units. In these systems, the yard is 36 inches and the foot is 12 inches, providing a straightforward relationship between units used for lengths, heights, and dimensions.

Subdivisions and usage: The inch is traditionally divided into halves, quarters, eighths, and sixteenths for practical measurement, especially in construction and carpentry. In engineering and manufacturing, decimal inches are common, such as 0.375 in. A related unit, the mil (or thou), equals 0.001 inch and is used for tolerances and film thickness.

History and etymology: The name inch derives from the Latin uncia, meaning a twelfth part, via Old English ynce. Historically, the inch originated as 1/12 of a foot, and older English measures sometimes used the barleycorn as a subunit, with the proverb three barleycorns making an inch reflecting long-standing tradition.

Modern usage: Inches remain standard in the United States for most everyday lengths, furniture, clothing sizing, and screen measurements. In many other parts of the world, metric units are official, with inches appearing mainly in industry, product specifications, and certain consumer contexts.