µm

µm

Micrometre
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Micron” redirects here. For other uses, see Micron (disambiguation).
Microscale” redirects here. For other uses, see Microscale (disambiguation).
For the measuring instrument, see Micrometer.
1 micrometre = SI units
1.000×10−6 m 1.0000 μm
US customary / Imperial units
3.281×10−6 ft 39.37×10−6 in

A micrometre (or micrometer) is by definition 1×10−6 of a metre (SI Standard prefix “micro” = 10−6). In plain English, it means one-millionth of a metre (or one-thousandth of a millimetre, 0.001 mm, or about 0.000039 inches). Its unit symbol in the International System of Units (SI) is μm. The latter may be rendered as um if Greek fonts are not available or not admissible. “Micron” comes from Greek: μικρόν mikrón, which means “small”.

The term micron and the symbol μ, representing the micrometre, were officially accepted between 1879 and 1967, but officially revoked by the ISI in 1967.[1] In practice, “micron” is a widely used term in preference to “micrometre” in many English-speaking countries, and in American English the use of the term helps differentiate the unit from the micrometer, a measuring device, which would otherwise be spelled as a homonym with micrometre.[dubious – discuss] The term “micron” has particular currency in science, and is extensively used in most English-speaking countries in the fields of geology, biology, physics, astronomy, machining, and the semiconductor industry.

The micrometre is a common unit of measurement for wavelengths of infrared radiation.[2]