An angle protractor is a tool used for measuring angles in degrees. It typically has a flat, semi-circular or circular shape with a scale marked in degrees (from 0° to 180° or 0° to 360° depending on the type). To use it, you align the center hole with the vertex of the angle and the arms of the protractor with the sides of the angle. The protractor then allows you to read the angle measurement directly from the scale.