Thou to Inches (thou to in)

1 thou equals 0.001 inches exactly.

1 thou = 0.001 inches

How to convert thou to inches

To convert thou to inches, multiply the number of thou by 0.001. This factor is exact. To go the other way, multiply inches by 1,000.

inches = thou × 0.001

Example: 10 thou = 0.01 inches.

About these units

Thou (thou)

US & ImperialCurrent unit

One thousandth of an inch (0.0254 mm), also called a mil. Used in machining, plastics and the thickness of films and wire.

Machinists say a part is out by a few thou, and the word is a clipping of thousandth, keeping only the first syllable. In North America the same length is often called a mil, which is easy to confuse with a millimetre in international drawings. One thou is a thousandth of an inch, which is exactly 0.0254 mm or 25.4 micrometres, so about 39 of them fit in a millimetre. The word is both singular and plural.

Joseph Whitworth pressed in 1857 for engineers to think in decimal thousandths instead of fractions of an inch, a habit that needed vernier calipers and micrometers to put into practice. Today the unit describes the thickness of paper, foil, wire, plastic sheet and paint films, with a plastic ID card about 30 thou thick. It also appears in older spark-plug gaps, gasket thicknesses and circuit-board geometry. For finer work, a tenth, meaning 0.0001 inch or 2.54 micrometres, is common, and gauge blocks are often given in millionths or in micrometres.

1 thou = 0.0000254 meters (exactly).

Sources: Wikipedia: Thou (unit); Wiktionary: thou

Inch (in)

US & ImperialCurrent unit

1/12 of a foot. Defined as exactly 25.4 millimeters since 1959, when the US and Commonwealth countries agreed a common international inch.

Latin uncia, meaning one-twelfth, is the root of both inch and ounce, and it passed into Old English as ynce. Roman measurers divided their foot into twelve unciae, and the English inch kept that twelfth. After 1066 an inch was reckoned as three barleycorns, and a 1324 statute attributed to Edward II spelled out the definition as three grains of barley, dry and round, placed end to end lengthwise. For centuries the inch was simply a twelfth of a foot, or a thirty-sixth of a yard, and the US and UK each kept their own copy of the standard yard.

Those copies differed slightly until the 1959 international agreement fixed the yard at exactly 0.9144 meter, which made the inch exactly 25.4 millimeters. The US adopted it in 1959 and the UK ratified it in 1963, effective 1964. Today the inch is still the customary unit in the United States and Canada, and the UK keeps it on road signs. Worldwide it also names display diagonals, wheel rims, tire codes and pipe sizes.

1 inch = 0.0254 meters (exactly).

Sources: Wikipedia: Inch; Wikipedia: Yard; NIST Guide to the SI, Appendix B.8: conversion factors

Related conversions

See all length units.