Micrometre

micrometre
A 6 μm diameter carbon filament above a 50 μm diameter human hair
General information
Unit system	SI
Unit of	length
Symbol	μm
Conversions
1 μm 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;^[1] SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron,^[2] 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).^[1]

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,^[1] and for grading wool by the diameter of the fibres.^[3] The width of a single human hair ranges from approximately 20 to 200 μm.