Radian Measure

Radian is the SI unit of angle. 1 radian = angle subtended at center by arc equal to radius. π radians = 180°. Conversion: radians = degrees × π/180. Degrees = radians × 180/π. Key values: 0°=0, 30°=π/6, 45°=π/4, 60°=π/3, 90°=π/2, 180°=π, 270°=3π/2, 360°=2π.