A kind of engineering method for calculating the gear cross sectional area was put forward. Comparing with the calculating result of the accurate method presented in CAD, the method is simple with less than 1% relative error. The gear volume was calculated through this algorithm and the gear solid was constructed by Pro/E software in order to check the outcome of above algorithm. The relative error was also less than 1%. On this basis，a series of experiment researches were carried out. The volume of billet was decided according to this algorithm and the geometries of final forged gear met the demands. The conclusion proves that this algorithm possesses high precision, which is entirely consistent with the voice of engineer and is worthy to be promoted.