How much does steel weigh per cubic millimeter?

Given that the density of mild steel is approximately 7.85 g/cm3m and 1 cubic millimetre is 1/1000 of a cubic cenimetre, the weight of one cubic millimetre of mild steel is 7.85/1000 = 0.00785g i.e. 7.85 milligrammes. -- Kev Gill