Protractor/prəˈtræktər,prəʊˈtræktər/ Definition 1 of 1Pro Tip 1/3Math Instrument A protractor is specifically used in mathematics or drawing to work with angles. We used a protractor in geometry class to draw precise angles. Pro Tip 2/3Semi-Circle Shape Protractors are commonly semi-circular but can be full circles, called 360-degree protractors. For a full rotation, we needed a 360-degree protractor. Pro Tip 3/3Measurement Unit Protractors measure angles in degrees, a unit for measuring the size of an angle. The protractor showed that the angle was 45 degrees.