The builder's square aids in cutting sheet material, such as full sheets of plywood, and in particular reduces the time required for cutting. The square comprises a short leg and a long leg connected in an L-shape. The short leg is of greater height than the long leg so that it can bear against one edge of the sheet of plywood to be cut. There is a clamping member at the distal end of the long leg so that the square can be clamped to the plywood. The builder's square also provides improved accuracy and safety for the user.
