Equal to 0.075 mm To know how many millimeters 75um is equal to, we need to know the conversion relationship between micron and millimeter. The relationship between um and mm can be expressed by the following mathematical formula: 1mm equals 1000um. This formula tells us that micron units can be converted into millimeter units. To know how many millimeters 75um is equal to, we only need to divide 75 by 1000, and the calculation result is: 75um is equal to 0.075mm