Protractor is a device for measuring the size of angles or drawing angles of specified sizes. Protractors are made of plastic, paper, or metal. Most protractors are shaped like the letter D, with the arc in the shape of a semicircle. Lines and numbers on the arc indicate angles from 0 to 180 degrees (or, in some cases, from 0 to 3,200 mils).
To measure an angle, a straight edge of the protractor–or a line printed on it–is placed along one line of the angle. The reading is made where the other line crosses the arc. Full-circle protractors can read from 0 to 360 degrees.
