microns

Micron, symbol μm, is a unit of length equal to one millionth of a meter. It is also commonly referred to as a micrometer, though the official SI unit name is the micrometer. The micron is not a base SI unit, but it is accepted for use with the SI and is widely used in science and engineering. One micrometer equals 10^-6 meters, and there are 1,000,000 μm in a meter. A nanometer is one thousand times smaller; thus 1 μm equals 1000 nm.

Micrometers are used to describe dimensions at the cellular and micro-scale. For instance, human red blood cells are about 7–8 μm in diameter; many bacteria range from about 0.5–5 μm; hair shaft diameters are on the order of tens of micrometers. Wavelengths of visible light fall roughly in the 0.4–0.7 μm range, while microfabrication and MEMS operate in the micrometer regime.

Devices and measurements: measurement tools include opto-mechanical micrometers and optical or electron microscopes that can resolve sub-micrometer features. The term micron is often used in biology, environmental science, and engineering contexts, while the micrometer is preferred in formal SI usage. The unit is central to discussions of particle sizes, film thicknesses, and microscopic scales.