Nov 17, 2022 · A “mil” is 1/1000th of an inch. This can sometimes mean a millimeter to people outside of the United States, so don’t get nfused! Gauge is (100) x (mils), so for example 0.3 mils = 30 gauge. To go from mils to microns, you multiply mils x 25.4. SolveTech makes thickness gauging technology for measuring plastic film.