Method for calculating material sizes

A method for calculating material sizes is used for calculating a sheet metal part. The sheet metal part is at least provided with a first part, and the first part is provided with a first section, a second section and a first bent section, wherein the first bent section is placed between the first section and the second section and is provided with a first extending part. The method for calculating material sizes comprises the steps that whether the sheet metal part is provided with the first part or not is detected; the coordinate plane where the first section is located is used as a datum face according to the selection of a user; the first part is unfolded and flattened to the datum face; the first material sizes of the first section, the second section and the first bent section with the first extending part being deducted are calculated. According to the method for calculating material sizes, the needed materials of the sheet metal part can be cut conveniently, and the cost needed by the materials of the sheet metal part can be more precisely calculated.