A 'micrometre' (
American spelling: 'micrometer'; symbol 'µm') is an
SI unit of
length equal to one
millionth of a
metre, or equivalently, one thousandth of a
millimetre. It is also commonly known as a 'micron'. It can be written in
scientific notation as 1×10
−6 m, meaning 1 / 1,000,000 m.
The symbol µm's character µ (
Unicode character U+00B5;
HTML µ) is the "
micro sign", which should look identical to the
Greek letter mu (μ) (the two may or may not look the same, depending on the
font). The symbol "um" is sometimes used, when the µ and μ are not available, for example in
ASCII, or when using a
typewriter.
The micrometre is a common unit of
measurement for
wavelengths of
infrared radiation. Some people (especially in
astronomy and the
semiconductor industry) use the old name micron and/or the solitary symbol µ (both of which were official between 1879 and 1967) to denote a micrometre. This practice persists in the face of official discouragement, perhaps to help disambiguate between the ''unit'' of measurement and the
micrometer, a measuring ''device''.
See also
★
1 E-6 m (for a comparative description of the micrometer in the context of other orders of magnitude)
★
SI
★
SI prefix
★
Metric system
★
Orders of magnitude
★
Micrometer (device), a tool that measures the thickness of objects.
★
Micronization