Circle Area & Circumference Calculator
Calculate the area, circumference, and diameter of a circle from its radius, in metric or imperial units.
Area
78.54
Breakdown
- Circumference
- 31.42
- Diameter
- 10
- Area unit
- cm²
- Length unit
- cm
Last updated:
FAQ
What is the formula for the area of a circle?
A = πr², where r is the radius. If you know the diameter d instead, use A = π(d/2)².
How do I find the circumference?
C = 2πr, or C = πd if you know the diameter.
Why is the area of a circle πr²?
π is the ratio of circumference to diameter, so sweeping the radius squared around the full rotation covers exactly π r² — a proof dating back to Archimedes.
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