A micrometre is smaller than a millimetre according to the metric system. Micrometers are also known as microns, and one millimetre is equal to 1,000 microns. The average width of a human hair is 40 to 50 microns, or 0.04 millimetre, while the average length of a dust mite is 400 microns, or 0.4 millimetres.
The metre is multiplied or divided by powers of 10 to represent various units in the metric system. The micron (1 x 10-6 m), nanoscale (1 x 10-9 m), picometer (1 x 10-12 m), and femtometer (1 x 10-15 m) are units smaller than the millimetre.