Circumference to Radius Calculator
Convert between a circle's circumference and radius, in either direction.
Circumference to Radius Calculator
Our Circumference to Radius Calculator converts between a circle's circumference and radius in either direction — enter one, and instantly get the other. Handy when it's easier to measure the distance around something (a tank, pipe, table, or wheel) than to measure straight to its center.
The Relationship Between Circumference and Radius
A circle's circumference is always 2π (approximately 6.2832) times its radius. Wrap a tape measure around a circular object, divide the reading by 2π, and you get the radius — without ever measuring to the center.
Conversion Formulas
Radius → Circumference: c = 2π × r
Example Calculations
Circumference → Radius: c = 31.42
r = 31.42 ÷ (2 × π) ≈ 5
✓ Radius ≈ 5
Radius → Circumference: r = 5
c = 2 × π × 5 ≈ 31.42
✓ Circumference ≈ 31.42
Features of Our Circumference to Radius Calculator
Who Can Use This Calculator?
👉 Try our Circumference to Radius Calculator to convert either measurement in seconds.