You may have noticed that there are buttons on your scientific calculator labelled "DEG", "RAD", and "GRAD". You may have wondered, what do they mean?
A degree (the usual symbol is °.) is 1⁄360 of the angle of a circle. A right angle is 90°.
A radianis 1⁄2π of a circle, so 1 rad is approximately equal to 57.296°. If you take two radii of a circle with radius 1 where the angle measurement between the two is 1 rad, the length of the arc of the circle with endpoints being the endpoints of the radii will be 1 as well. A gradian is sometimes known as a metric degree. A right angle (90°) is defined as 100 gradians, so a full circle (360°) would be 400 gradians. Gradians are not as commonly used as degrees or radians are.