Micrometre

"Micron" redirects here. For other uses, see Micron (disambiguation).

"Microscale" redirects here. For other uses, see Microscale (disambiguation).

For the measuring instrument, see Micrometer (device).

"μみゅーm" redirects here. For the chemical unit "μみゅーM", see Micromolar.

micrometre
A 6 μみゅーm diameter carbon filament above a 50 μみゅーm diameter human hair
General information
Unit system	SI
Unit of	length
Symbol	μみゅーm
Conversions
1 μみゅーm in ...	... is equal to ...
SI base units	10−6 m
Natural units	1.8897×104 a0
imperial/US units	3.9370×10−5 in

The micrometre (Commonwealth English) as used by the International Bureau of Weights and Measures; SI symbol: μみゅーm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System of Units (SI) equalling 1×10⁻⁶ 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 0.00004 inch).

The nearest smaller common SI unit is the nanometre, equivalent to one thousandth of a micrometre, one millionth of a millimetre or one billionth of a metre (0.000000001 m).

The micrometre is a common unit of measurement for wavelengths of infrared radiation as well as sizes of biological cells and bacteria, and for grading wool by the diameter of the fibres. The width of a single human hair ranges from approximately 20 to 200 μみゅーm.

Examples

How big is 1 micrometre?

Between 1 μみゅーm and 10 μみゅーm:

• 1–10 μみゅーm – length of a typical bacterium
• 3–8 μみゅーm – width of strand of spider web silk
• 5 μみゅーm – length of a typical human spermatozoon's head
• 10 μみゅーm – size of fungal hyphae
• about 10 μみゅーm – size of a fog, mist, or cloud water droplet

For more examples of things measuring 1 to 10 micrometres, see Orders of magnitude (length) § 1 micrometre.

Between 10 μみゅーm and 100 μみゅーm:

• about 10–12 μみゅーm – thickness of plastic wrap (cling wrap)
• 10 to 55 μみゅーm – width of wool fibre
• 17 to 181 μみゅーm – diameter of human hair
• 70 to 180 μみゅーm – thickness of paper

For more examples of things measuring 10 to 100 micrometres, see Orders of magnitude (length) § 10 micrometres.

SI standardization

The term micron and the symbol μみゅー were officially accepted for use in isolation to denote the micrometre in 1879, but officially revoked by the International System of Units (SI) in 1967. This became necessary because the older usage was incompatible with the official adoption of the unit prefix micro-, denoted μみゅー, during the creation of the SI in 1960.

In the SI, the systematic name micrometre became the official name of the unit, and μみゅーm became the official unit symbol.

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. In spoken English, they may be distinguished by pronunciation, as the name of the measuring device is often stressed on the second syllable (/maɪˈkrɒmɪtər/ my-KROM-it-ər), whereas the systematic pronunciation of the unit name, in accordance with the convention for pronouncing SI units in English, places the stress on the first syllable (/ˈmaɪkroʊmiːtər/ MY-kroh-meet-ər).

The plural of micron is normally microns, though micra was occasionally used before 1950.

Symbol

See also: Micro- § Symbol encoding in character sets

The official symbol for the SI prefix micro- is a Greek lowercase mu. In Unicode, there is also a micro sign with the code point U+00B5 (µ), distinct from the code point U+03BC (μみゅー) of the Greek letter lowercase mu. According to the Unicode Consortium, the Greek letter character is preferred, but implementations must recognize the micro sign as well. Most fonts use the same glyph for the two characters.

See also

• Metric prefix
• Metric system
• Orders of magnitude (length)
• Wool measurement

External links

• The dictionary definition of micrometre at Wiktionary