micrometers

Micrometers are units of length in the metric system, equal to one millionth of a meter (1 μm or 10^-6 m). The symbol μm is widely used in scientific contexts. The term micron is a historical or informal alternative name for the unit. In many applications, micrometers are used to express dimensions at the scale of cells, fibers, and thin films.

As a scale, 1 mm = 1000 μm and 1 μm = 1000 nm. The thickness of a human hair ranges from about 30 to 100 μm, while red blood cells are typically 6–8 μm in diameter; many bacteria are approximately 0.5–5 μm in size.

As instruments, micrometers refer to precision measuring devices known as micrometer screw gauges. These devices measure external dimensions by turning a calibrated screw and reading a sleeve scale together with a thimble scale. Readings commonly have resolutions of 0.01 mm (10 μm) or 0.001 mm (1 μm) in higher-end instruments. There are also internal micrometers for holes and depth gauges and digital variants that display measurements electronically.

Measurements using micrometers are subject to temperature effects and require calibration against standards. The SI unit reference is the meter, and measurements are often reported with appropriate uncertainty. The micrometer unit remains essential in manufacturing, metrology, and the natural sciences for characterizing small features with precision.