Thou (length)

Thou (length)

A thousandth of an inch is a derived unit of length. Equal to 0.001 inch, it is normally referred to as either a thou ( /ˈθaʊ/), a thousandth, or (particularly in the United States) a mil.

The plural of thou is also thou (thus one hundredth of an inch is "10 thou"), while the plural of mil is mils (thus "10 mils"). Both words come from roots meaning "1000": "thou" from the English "thousand", which is from the Germanic root for 1000, and "mil" from the Romance root for 1000.