Casting of iron or steel is performed by assembling a charge (1) of plate-like charge elements (1a, 1b, 1c . . . ) with known compositions and dimensions by placing them on top of each other, and of an alloying component entity (2) with known composition, such as alloying component pieces or an alloying component cartridge, by means of which the composition of the charge is balanced to the desired precise composition. The charge is melted in a furnace (5) and cast to form a casting with an exactly known composition.