How Do I Find Arc Length From Angle & Radius?

An arc is a set section of a circle's circumference, separated by two points. The arc can be measured using the values of its central angle and its radius, which is the length from the center of the circle to any point on the circumference.

Angle in Radians

• Multiply the measurement of the angle in degrees by π, which is a mathematical constant that begins with 3.14, and then divide that number by 180. For example, if the angle was 60 degrees, then the result would be 60π/180, which is π/3.

Multiply the Radius

• Multiply that number by the radius. In the previous example, the radius is 4 feet, and multiplying it by π/3 results in 4π/3.

Find the Length

• Solve that number for its decimal representation. In the previous example, 4π/3 equals 4.18. The length of the arc is therefore 4.18 feet.