micrometres

The micrometre (symbol μm; plural micrometres) is the SI unit of length equal to 10^-6 metres. The prefix micro- denotes a factor of one millionth. Therefore, one micrometre is equal to 1,000 nanometres.

Micrometres are used to express dimensions at the microscopic scale in physics, chemistry, biology, and engineering. Typical sizes include bacteria around 0.5–5 μm, many human cells near 10 μm, and ordinary hair diameters about 50–100 μm. Infrared wavelengths span roughly 3–100 μm, and microfabrication features are often described in micrometres.

The term micrometre is the standard SI unit for small lengths. The word micron is a common non-SI alternative used historically or in some fields. In American English, micrometer can refer to either the unit or the measuring instrument, which can lead to ambiguity; context usually clarifies.