The acute angle is greater than 0° but less than 90°. 0° * α * 90°. The rigth angle has a measure of 90°. Denoted by a square inside the angle. α = 90°. The obtuse angle is greater than 90° but less than 180°. 90° * α * 180°. The stright angle has a measure of 180°. The first arm with second creates the stright line. α = 180°. The reflex angle is greater than 180° but less than 360°. 180° * α * 360°. The full angle has a measure of 360°. The second arm covers the first arm. α = 360°.