The micrometre (International spelling as used by the International Bureau of Weights and Measures; SI symbol: µm) or micrometer (American spelling), also commonly known as a micron, 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, or if the writer is not aware of the distinction.
The micrometre is a common unit of measurement for wavelengths of infrared radiation as well as sizes of cells and bacteria and is also commonly used in plastics manufacturing.[1]
Micrometres are the standard for grading wool (referring to the diameter of wool fibres). Any wool finer than 25 µm can be used for garments, while coarser grades are used for outerwear, rugs and carpets.
The symbol for the SI prefix micro-, µ, is a Greek lowercase mu, μ. In Unicode, it has the codepoint U+00B5, distinct from that of the Greek letter lowercase mu so that machines can recognize it as the SI prefix symbol rather than as a letter. Many fonts use the same glyph for the two characters.
