To help compare different orders of magnitude, this page lists lengths between 10â4 m and 10â3 m (100 Âµm and 1 mm). 1  100 Âµm â 1/10 of a millimetre. 2  100 Âµm â 0.00394 inches. 3  100 Âµm â average diameter of a strand of human hair.  100 Âµm â thickness of a coat of 1  paint. 100 Âµm â length of a dust particle.