○ Circumference of a Circle Calculator

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Circumference Formula

The circumference is the perimeter of a circle — the total distance around its edge. It is directly proportional to the diameter through the constant π (pi).

C = 2πr = πd (π ≈ 3.14159)
From area: r = √(A/π), then C = 2πr

Pi (π) Explained

π (pi) is the ratio of any circle's circumference to its diameter: π = C/d ≈ 3.14159265... It is an irrational number — its decimal representation never ends or repeats.

Frequently Asked Questions

What is the circumference of a circle with radius 7? ▼
C = 2 × π × 7 = 14π ≈ 43.98 units.
How do you find circumference from diameter? ▼
C = π × d. For diameter 10: C = π × 10 ≈ 31.42 units.
What is π (pi)? ▼
Pi (π) is the mathematical constant equal to the ratio of a circle's circumference to its diameter: approximately 3.14159265358979...