mikrometre

The micrometre, sometimes written micrometre or mikrometre, is a unit of length in the metric system equal to one millionth of a metre. Its symbol is μm, derived from the Greek letter mu and the word metre. Because the SI prefix micro denotes 10^-6, 1 μm equals 10^-6 metres, which is 0.001 millimetres or 1000 nanometres.

The micrometre is used widely in science, engineering, and medicine to express dimensions at the microscopic scale. Bacterial widths typically fall within about 0.5 to 2 μm, and many eukaryotic cells range from roughly 10 to 100 μm in diameter. In microfabrication and optoelectronics, feature sizes and tolerances are commonly specified in micrometres.

The term can be confused with the measuring instrument known as a micrometer (also called a screw gauge), which is used to measure small lengths with high precision. Spelling varies by language and region; micrometre is common in many varieties of English and other languages, while micrometer is often used in American English for both the unit and the instrument. The universal standard is the symbol μm, which remains the same across contexts.

See also: nanometre, millimetre, micrometer (instrument).