Micrometer (unit of length)

Comparison of human hair (in light grey) with 50 μm diameter and carbon filament 6 μm diameter.

The micrometer, micron or micron is a unit of length equal to one thousandth of a millimeter. Its symbol is µm. Its name comes from the Greek μικρόν (micrón), neuter of μικρός (micrós): small.

Other names

The micrometer is also called:

• Micron (plural: microns), symbolized μm.
• Micra (plural: microns; plural in Greek: micron)also symbolized μm. In etymological rigor, this should be the informal plural when the full word (micrometer) is not used, because already plural.

In mechanical manufacturing, the "micron" is the smallest unit of length, in which the dimension tolerances of the parts that are subjected to rectification are expressed.

Equivalences

One micrometer equals:

• One millimeter: 1 μm = 0.001 mm = 1 × 10^-3mm
• One millionth of a metre: 1 μm= 0,000 001 m = 1 × 10^-6m
• A thousand nanometers: 1 μm = 1000 nm

1 mm = 1000 μm

1 m = 1 000 000 μm

1 nm = 0.001 μm

Examples

The diameter of human hair ranges from 70 to 80 µm.

Particles that are less than 10 micrometers in diameter are called PM10.

Fine particles are less than 2.5 micrometers in diameter and are called PM 2.5.

Submicron particles have a diameter less than 1 μm and are called PM 1.

Microfine particles have a diameter less than 0.1 μm and are called PM 0.1.

Human lungs can only remove particles larger than 0.2 micrometers. Smaller particles can reach any part of the body and cause damage and tumors.