A radian is a unit of measurement used to measure angles. It is the standard unit of angular measure used in many areas of mathematics. One radian is defined as the angle subtended from the center of a circle which intercepts an arc equal in length to the radius of the circle. More generally, the magnitude in radians of a subtended angle is equal to the ratio of the arc length to the radius of the circle. A full angle is equal to 2π radians. Radians are preferred by mathematicians because they are based on the pure idea of "the radius being laid along the circumference". Small angles are often measured in radians because the values of the sine and tangent functions get close to the value of the angle in radian. To convert radians to degrees, we multiply the angle by 180/π.