Circumference Calculator
Get the perimeter of any circle instantly. Enter the radius, diameter or even the area, and the calculator works out the circumference for you - with each step of the formula shown.
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How to use
- Select whether the value is the radius, diameter or area.
- Enter the value.
- The circumference will show with steps.
Tips
- Circumference is just 2 times pi times the radius - easy to sanity-check the result.
- If you know the diameter, multiply by pi directly (about 3.14).
- Starting from area? The tool reverses the area formula for you - no square roots by hand.
- Keep units consistent: radius in meters gives circumference in meters.
Note: Formula: C = 2 pi r = pi x d. The ratio of circumference to diameter is always pi (3.14159...), no matter how big the circle is.