Math calculator
Circumference Calculator
Circumference, radius, diameter, and area of a circle from any one value.
Quick answer
How do you find the circumference of a circle?
Multiply the diameter by π, or the radius by 2π. A circle with radius 5 has C = 2 × π × 5 ≈ 31.42. A circle with diameter 10 has the same circumference: π × 10 ≈ 31.42.
C = 2πr = πd • d = 2r • A = πr² • r = C ÷ 2π
⚡ Answer updates as you type · Enter = calculate · Esc = reset
- r = 5
- C = 2πr = 2 × π × 5 = 31.4159
- d = 2r = 10
- A = πr² = 78.5398
Enter a radius, diameter, circumference, or area to get every measurement of the circle.
About this Circumference Calculator
The Circumference Calculator works out the distance around a circle from its radius, diameter, or area — or goes backward from the circumference. It shows all four circle measurements at once with the formulas filled in.
What you'll need
- • Radius, diameter, circumference, or area
How it works
- 1. Choose what you know.
- 2. Enter the value.
- 3. Read circumference, radius, diameter, and area.
- 4. Check the formula steps.
- 5. Units match what you entered.
Worked example
A 12-inch pizza (diameter 12): circumference = π × 12 ≈ 37.70 in, area ≈ 113.10 in².
Related searches
Circumference Calculator FAQ
What is the Circumference Calculator?
The Circumference Calculator is a free online tool that helps you circumference, radius, diameter, and area of a circle from any one value.
How do I use the Circumference Calculator?
Open the Circumference Calculator, enter the requested values, and review the instant estimate on the page.
Is the Circumference Calculator free?
Yes. The Circumference Calculator is free to use on Fast Online Calculator and does not require an account.
What is π?
Pi (≈ 3.14159) is the ratio of any circle's circumference to its diameter.
How do I find the radius from circumference?
Divide by 2π. A circumference of 31.42 gives r ≈ 5.
Is circumference the same as perimeter?
Yes — circumference is the perimeter of a circle.
How do I find diameter from area?
d = 2√(A ÷ π). An area of 78.54 gives d ≈ 10.
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