Circle Circumference Calculator
Calculate the circumference of a circle from its radius or diameter. Also shows the area instantly.
Circumference
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Area
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Radius / Diameter
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Circumference Formulas
C = 2 × π × r (from radius)
C = π × d (from diameter)
C = π × d (from diameter)
The circumference is the distance around the outside of a circle — its perimeter.
Example: A circle with radius 7
Circumference = 2 × π × 7 = 14π ≈ 43.9823 units
Area = π × 49 ≈ 153.9380 square units
Circumference = 2 × π × 7 = 14π ≈ 43.9823 units
Area = π × 49 ≈ 153.9380 square units
Circumference vs Area
| Property | Formula | Unit |
|---|---|---|
| Circumference | 2πr | Linear (cm, m, in) |
| Area | πr² | Square (cm², m², in²) |
Frequently Asked Questions
What is the relationship between circumference and diameter?
The ratio of circumference to diameter is always π (≈ 3.14159). This is actually the definition of π: C/d = π.
How do I find the radius from the circumference?
Rearrange the formula: r = C / (2π). Divide the circumference by approximately 6.2832.
Is circumference the same as perimeter?
Yes, circumference is the specific term for the perimeter of a circle. Both measure the distance around the boundary of a shape.
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Last updated: 2026-08-08