Circumference calculator
Calculator
The calculator needs JavaScript. The tables below give the same numbers for common cases.
How it is worked out
- Radius r = 5.
- Diameter = 2r = 10.
- Circumference = 2πr = 31.415927.
- Area = πr² = 78.539816.
| Inputs | Answer |
|---|---|
| You know the: Radius; Radius: 5; Diameter: 10; Circumference: 31.4159; Area: 78.5398 | A circle with radius 5 has circumference 31.415927 and area 78.539816. |
| You know the: Diameter; Radius: 5; Diameter: 7; Circumference: 31.4159; Area: 78.5398 | A circle with radius 3.5 has circumference 21.991149 and area 38.48451. |
| You know the: Area; Radius: 5; Diameter: 10; Circumference: 31.4159; Area: 50 | A circle with radius 3.989423 has circumference 25.066283 and area 50. |
How to use it
The circumference is the distance around a circle: C = 2πr = πd. Dividing the circumference by the diameter always gives π, about 3.14159.
You can start from the radius, the diameter, the area or even the circumference itself; the calculator returns all four measurements.
Frequently asked questions
What is the circumference of a circle with radius 5?
2 × π × 5 ≈ 31.416.
How is circumference related to diameter?
Circumference = π × diameter.
How do I find the circumference from the area?
Find r = √(A ÷ π), then C = 2πr.
Method: standard arithmetic shown step by step; no outside data is used. Checked 2026-11-12.
Written by Calculators Free Editorial Team · Data checked 2026-11-12
About · How we verify this · Editorial policy · Corrections
About · How we verify this · Editorial policy · Corrections
General information only. Results are plain arithmetic on the numbers you enter; check anything important (money, health, school work) against your own records or the official source.