Circumference of Circle Calculator

Calculate circle circumference from radius or diameter. Free online circumference calculator with pi formula.

The Circumference of Circle Calculator finds the perimeter (distance around) of any circle using the radius or diameter. Using the formula C = 2πr or C = πd, this essential geometry tool helps with wheel rotations, circular borders, belt lengths, and any application involving the outer edge of circular shapes.

Common use cases

  • Tire and wheel calculations
  • Belt and rope length estimation
  • Circular fencing requirements
  • Track distance calculations
  • Decorative border planning

How to use

  1. Enter the radius OR diameter
  2. Select which measurement you're providing
  3. Click calculate for circumference
  4. View the calculation with π
  5. Copy the precise result

FAQ

What is the circumference formula?

C = 2πr (using radius) or C = πd (using diameter), where π ≈ 3.14159.

What is pi (π)?

Pi is the ratio of any circle's circumference to its diameter, approximately 3.14159...

How many rotations for a distance?

Rotations = Distance ÷ Circumference. A wheel with 2m circumference makes 50 rotations per 100m.

What's the relationship between circumference and area?

Both depend on radius: C = 2πr and A = πr². Area grows faster (quadratically) than circumference (linearly).