How to Measure Angles to Frame a Wall

Place two wooden boards of the same width and thickness horizontally along both sides of your outside wall corner so that the ends of the boards overlap one another. Extend the bottom board about 1 inch past the top, at the point of overlap. Use your pencil to trace the outline of the bottom board's two edges onto the top board.

Remove the boards from the wall, and use your pencil to draw a line from the corner of one pencil line, to the opposite corner of the other. The result will be a diagonal guide, which will provide an even miter cut. The miter cut will be fitted to the wall corner, and will allow for the flush installation of molding or other wall additions.

Lay the marked board onto the unmarked board, so the two are perfectly even. Use your miter box and saw to cut along the pencil line. Flip one of the boards over after the cut is made, and fit the two together. The boards can then be used as templates for cutting material around the corner.

Use your speed square or protractor to mark the wall material to the proper angle, once the measurement has been taken. Speed squares and protractors both have degree markings stamped onto them. While the speed square has degree marking along its straightedge length, and protractors have degree markings set within their curved frame, the principle and function is the same. Place the measuring device onto your wall material with the set point along the straightedge of the material. Line the degree markings up with the desired angle size, and mark.

Place your sliding T-bevel over the outside or inside corner on your wall. Loosen wing nut that fastens the blade and the handle together. Move the blade and handle until the the bevel fits snugly around or within the wall angle. Tighten the wing nut to hold the angle as set. Place the T-bevel onto a protractor and read the angle size. The T-bevel can also be placed directly onto your lumber, and the angle can be traced for cutting.