What is a Micrometer?

The micrometer (also called micron) equals one millionth of a meter (0.000001 m) and is the standard unit for measuring extremely small dimensions in science, biology, and technology. Visible light wavelengths range from about 0.4 to 0.7 µm, and the diameter of a human red blood cell is 6–8 µm. The micrometer is critical in air-quality monitoring (PM2.5 refers to particles smaller than 2.5 µm), microfabrication (older semiconductor processes were measured in microns), and biology (bacterial sizes range from 0.5 to 10 µm). The Greek letter µ (mu) represents 'micro,' the SI prefix for one millionth. The unit relates to the millimeter (1,000 µm = 1 mm) and the nanometer (1 µm = 1,000 nm). Modern semiconductor manufacturing has moved beyond micrometers to nanometer scales for transistor features.

Visual reference for how the micrometer relates to other length units. Each row links to the full converter for that pair.

See all 15 length units in matrix view →

• Air quality measurement (PM2.5, PM10)
• Cell biology and microscopy
• Thin-film coatings in electronics manufacturing

• ✓1 µm = 1/1000 mm = 1000 nm. Check which prefix is in your data source.
• ✓The micrometre is also called the micron in older literature; the symbol µm is the modern standard.
• ✓Visible light wavelength (400–700 nm) is 0.4–0.7 µm — useful for optics.

• ✗Confusing micrometre (length) with micrometer (measuring tool) — context usually makes it clear.
• ✗Using µm when the data is actually in nm — off by 1000×.
• ✗Treating PM2.5 as a concentration rather than a particle-size threshold.