Abstract: Based on the actual design of medium and small cylindrical steel tank, a method to calculate the height of the tank has been found. At the height the steel to be used is least. The method can be applied to uniform and variable shell thickness of the tank. It was found that the height is dependent not only on steel, welded seam and the thickness of the shell and bottom, but also on height of wall-plate, minimum shell thickness and vapour pressure. The height calculated by the old method is more than that by the paper. The height of different actual volume tank at uniform nominal volume should be a little different.