Circumference Calculator
Find the circumference of any circle instantly. Enter the radius, diameter, or an existing circumference measurement to get all the key properties. For example, a circle with radius 5 has a circumference of about 31.416 and an area of about 78.54.
Circumference Formulas
The circumference (perimeter) of a circle can be calculated two ways:
- From radius: C = 2πr
- From diameter: C = πd
Since the diameter is just twice the radius (d = 2r), these formulas are equivalent.
Finding Radius from Circumference
If you know the circumference and need the radius, rearrange the formula: r = C / (2π). A circle with circumference 31.416 has a radius of about 5.
Area of a Circle
This calculator also computes the area using A = πr². Knowing both circumference and area is useful for anything from sizing circular gardens to calculating pipe flow capacity.
Real-world example:
A running track's inner lane has a radius of 36.5 meters. Its circumference is 2 x π x 36.5 = 229.34 meters, which matches the standard 200m straight + two curves layout.