|1.0000×10−6 m||1.00000 μm|
|US customary / Imperial units|
|3.2808×10−6 ft||39.370×10−6 in|
|Look up micrometre in , the free dictionary.|
The micrometre (International spelling as used by the International Bureau of Weights and Measures; SI symbol: µm) or micrometer (American spelling) is an SI derived unit of length equaling 1×10−6 of a metre (SI standard prefix "micro-" = 10−6); that is, one-millionth of a metre (or one-thousandth of a millimetre, 0.001 mm, or about 0.000039 inch). The symbol µm is sometimes rendered as um if the symbol µ cannot be used.
The symbol for the SI prefix micro-, µ, is a Greek lowercase mu, μ. In Unicode, it has a codepoint distinct from that of the Greek letter lowercase mu so that it can be recognized as a symbol and not a letter. Many fonts use the same glyph for the two characters.
Nevertheless, in practice, "micron" remains a widely used term in preference to "micrometre" in many English-speaking countries, both in academic science (including geology, biology, physics, and astronomy) and in applied science and industry (including machining, the semiconductor industry, and plastics manufacturing). Additionally, in American English the use of "micron" helps differentiate the unit from the micrometer, a measuring device, because the unit's name in mainstream American spelling is a homograph of the device's name.