One millimetre equals exactly 1,000 micrometres (microns). To convert millimetres to microns, multiply by 1,000. To convert microns to millimetres, divide by 1,000. The micrometre (symbol μm) is the unit between the millimetre and nanometre in the SI scale: 1 mm = 1,000 μm = 1,000,000 nm = 10⁹ pm. Microns are the standard unit for: semiconductor lithography (modern chips at 3–7 nm node sizes, though these are marketing terms), medical device tolerances, fibre optics (single-mode fibre core diameter = 8–10 μm), and particle size in filtration.
One millimeter equals exactly 1,000 micrometers (μm), also called microns. Micrometers are the working unit for manufacturing tolerances, biological cell sizes, optical fiber diameters, and dust particle classification. A human hair is 50–100 μm in diameter; a red blood cell is about 8 μm; bacteria range from 0.5 to 5 μm; PM2.5 air pollution particles are 2.5 μm or smaller. Optical fiber cladding is typically 125 μm (0.125 mm) in diameter. Surface finish roughness (Ra) in machined parts is stated in micrometers or microinches. Converting mm to μm: multiply by 1,000. Converting μm to mm: divide by 1,000. Microscopy calibration, thin-film deposition targets, and semiconductor layer thicknesses are all specified in micrometers, requiring confident conversion from millimeter-scale engineering drawings to micron-scale process specifications.
