Circle Circumference Calculator
C = 2πr (or πd). Area = πr². The fundamental circle formulas.
Result
Circumference
31.415927
2π × 5 = 31.4159.
- Radius5.000000
- Diameter10.000000
- Circumference31.415927
- Area78.539816
- 2π6.28318531
Step-by-step
- Radius = 5.0000 (from input).
- C = 2πr = 2 × 3.141593 × 5.0000 = 31.4159.
- Area = πr² = 3.141593 × 25.0000 = 78.5398.
How to use this calculator
- Pick radius or diameter.
- Enter value.
- Read circumference + area.
About this calculator
A circle's circumference C = 2πr = πd. π ≈ 3.14159 — the ratio C/d is constant for every circle. Area scales as πr² — doubling radius quadruples area. Used in everything from wheels to pizza to satellite orbits. The number π itself was known to Babylonian and Egyptian mathematicians ~2000 BCE; Archimedes proved 3.140845 < π < 3.142857 around 250 BCE.
Frequently asked
It's the ratio of circumference to diameter — constant for any circle. Defined as C/d.
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