### Radians

**Abbreviation/Symbol:**

- rad
- c

**Unit of:**

- Angle

**Description:**

The radian is an SI derived unit of angle, commonly used in maths and engineering. A radian measures approx. 56.296 degrees (when the arc length is equal to the radius).

**Definition:**

The angle made by taking the radius of a circle and wrapping it along the circle's edge. Therefore 1 Radian is equal to (180/π) degrees

**Origin:**

Roger Cotes, a colleague of Isaac Newton who helped proofread the Principia, is credited with defining the Radian in 1714, although other mathematicians had been using angle measurements based on the length of the arc as far back as the 15th Century

**Common references:**

- π radians = 180 degrees. 2 * π radians = 360 degrees

**Usage context:**

Radians lend themselves to widespread use in maths. They are also commonly encountered in physics where they are used to measure angular velocity and accelaration.

**Component units:**

- Radians are sometimes subdivided into 100 centrads.

**Multiples:**

- There are 2 * π radians in a circle