According to the mathematical formula of object weight, we know that weight = density × volume. The density of steel is about 7.85g/cm3. So you can convert the volume into cm3 (because 1 m = 100 cm, 10 mm = 1 cm), and then use the above formula to calculate the weight. Steel plate volume V = length× width× height =1m×1m×10mm =100cm×1cm; V= 100000cm3. Substituting the volume value and density value into the formula, the weight of this steel plate is 78500g, which is equal to 78.5kg..