Often referred to as a "framing square," the carpenter square is an L-shaped tool commonly used to measure angles. Consisting of two extended arms of separate lengths, the body of a carpenter square forms a perfect right angle of 90 degrees, which allows for an easy and quick measurement of corners, steps and other structures utilizing a simple right angle. Though typically made of steel, carpenter squares can be made of many materials, from plastic to rust-resistant aluminum.
Look at the two arms that make up the carpenter square. The wider arm, typically 2 inches wide, is called the "blade," whereas the narrower arm is referred to as the "tongue."
While a great number of tools have the ability to measure lengths in centimeters and inches, the carpenter square provides a double-ruler of measurements imprinted along the sides. Familiarize yourself with the two sets of measurements imprinted on the inside and outside of the carpenter square: Each begins at zero and graduates upward in inches, centimeters and--depending on the make of your particular square--millimeters.
The carpenter square and its imprinted measurements can be very useful when measuring shorter measurements toward the end of a section of wood. The same function that the "lip" at the end of measuring tape fulfills in holding the tape in place, a carpenter square does by literally hooking the section with the smaller arm of the carpenter square resting over the edge of the board. This acts as a ruler stop and allows you to derive an exact measurement.
Angles and Squares
Practice measuring angles with the inside corner of your carpenter square. The primary function of the carpenter square is to measure and adjust angles and corner placements. From checking the factory edges of a particular section of wood to laying out rafters and stairs for construction, most simple right angles can be checked by inserting the carpenter square.
For example, when testing the proper factory edges of a particular board length, place the carpenter square at one corner of the board to test the right angle of each corner. If the corner is square, the two perpendicular edges will run evenly alongside the inside of the carpenter's square to the corner. Repeat this test on the opposite corner as well.
Carpenters in the process of framing a roof will often utilize the carpenter square to gather measurements for specific angle calculations involving the factors of hypotenuse, pitch and rafter length. For instance, when constructing a set of rafters for a level roof (all level roofs indicate a pitch of zero), a 45-degree angle as measured by the carpenter square should be utilized in rafter construction.
When building stairs, the carpenter square helps plan and lay out step treads of appropriate length. Using the outside measurements of the carpenter square, lay out each step of the desired rise and run length. For instance, if creating a set of stairs with an 8-inch rise ("rise" indicates the height one must raise one's foot to reach each step) with a 10-inch "run," or depth, place the carpenter square on a 2-by-12 piece of lumber and trace the outline of the square at the desired measurements. Slide the square up the board until the square rests on top of the previous measurement and repeat until each step has been traced out. In this process, the natural right angle of the square is used to help trace step treads, which are traditionally simple right angles, for cutting.