Circumference to Radius
Convert any circumference value to its radius instantly. Enter the circumference below and get the radius using the formula r = C ÷ (2π).
Circumference to Radius Formula
To find the radius from a known circumference, divide the circumference by 2π:
r = C ÷ (2π)
The radius r equals the circumference C divided by 2 times pi. 2π is approximately 6.28318.
For example, find the radius of a circle with a circumference of 31.42:
r = 31.42 ÷ (2π) = 5.0003
The radius of this circle is approximately 5.0003.
Frequently Asked Questions
Divide the circumference by 2π (6.28318). The formula is r = C ÷ (2π). For example, a circumference of 31.42 gives a radius of about 5.
r = 100 ÷ (2π) = 15.9155. The radius is approximately 15.92 units.
The circumference equals 2π times the radius (C = 2πr). Conversely, the radius equals the circumference divided by 2π. The radius is always half the diameter.