Convert Mil to Meter

A mil (also called a thou) is an Imperial unit of length equal to one thousandth of an inch (1/1000 in = 0.0254 mm = 25.4 μm exactly). It is used in engineering, manufacturing, and materials specifications.

The mil is derived from the Latin mille, "thousand," denoting one-thousandth of an inch. Standardized in industrial use during the 19th-century rise of precision engineering.

Mils are used to specify thicknesses of plastic films, foils, paper, copper traces on printed circuit boards (PCBs), wire insulation, and paint coatings. A standard sheet of paper is about 4 mils thick.

Adopted in 19th-century engineering practice; the value (1/1000 in) became exact in 1959 when the inch was fixed at 25.4 mm via the International Yard and Pound Agreement. The British term is "thou"; American term is "mil".

The meter is the SI base unit of length. Since 2019, the meter has been defined by fixing the numerical value of the speed of light in vacuum to exactly 299,792,458 meters per second. Every other SI length unit derives from the meter.

The meter was originally defined in 1793 by the French Academy of Sciences as one ten-millionth of the distance from the equator to the North Pole along a meridian through Paris. It has been redefined multiple times — by physical prototype, then by atomic transitions, and finally in 2019 by fundamental physical constants.

The meter is the international standard for length in science, engineering, construction, athletics, and everyday measurement in metric countries. It underpins definitions of area (m²), volume (m³), and most derived SI units.

Established 1793 in France; ratified internationally via the Metre Convention 1875; redefined in 1960, 1983, and most recently 2019 when the SI redefinition fixed it to the speed of light.