Microns
Abbreviation/Symbol:
μm
Unit of:
Worldwide use:
A micron is the older name for the micrometer (µm), one millionth of a meter. The word comes from the Greek mikros, meaning small, and it is still used for filter ratings, as in a 5 micron filter.
Coating thicknesses are given in microns – a sheet of printer paper is about 100 microns, ie 0.1mm.
Definition:
A micron, also known as a micrometer, is a unit of length in the metric system. It is equal to one millionth of a meter or 0.001 millimeters.
Origin:
The word micron comes from the Greek mikros, small. It was adopted in 1879 as the name for one millionth of a meter (0.001mm) and dropped as an official name in 1967 in favour of micrometer, symbol μm.
Common references:
Light dust particle = 1μm
Red blood cell = 8μm
Pollen grain = 15μm
Limit of what the naked eye can see: 10μm - 40μm
Grain of salt = 60μm
Human hair = 50μm - 180μm
Usage context:
Filters and particles are rated in microns: HEPA filters catch 99.97% of particles of 0.3 microns, a 0.2 micron filter is sterilising grade, and PM2.5 air pollution is particles under 2.5 microns across.