Calculator
Circumference Calculator
Type a radius or a diameter — we'll use π to compute the exact circumference of the circle.
How to calculate circumference
The circumference of a circle is the distance all the way around its edge. Two equivalent formulas use pi (π ≈ 3.14159…):
- From radius:
C = 2 · π · r - From diameter:
C = π · d
Because the diameter is just twice the radius (d = 2r), both formulas give the same answer. Pi is the ratio of a circle's circumference to its diameter — it's the same constant for every circle in the universe.
Worked example
A pizza has a radius of 15 cm. What's its circumference?
C = 2 · π · 15 = 30π ≈ 94.2478 cm
Tips
- Keep your units consistent. If radius is in inches, circumference is in inches.
- For exact answers, leave π symbolic (like
30π) instead of decimalizing. - Want to go the other way? Try our diameter to circumference converter.
Related calculators
- Arc length calculator — circumference of a partial arc.
- Reference angle calculator — reduce angles into standard position.
- Diameter to circumference — quick diameter conversion.