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Triangle Calculator
Solve any triangle from three sides or two sides and the angle between them: angles, area, perimeter and type.
Circumference Calculator
Find a circle’s circumference from its radius, diameter or area, plus the other measurements.
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How to use this calculator
Enter your values. The result updates as you type; press Calculate to confirm and jump to the result on mobile. Use Share to send the calculator with your result.
Circle formulas
C = 2πr = πd
A = πr²
r = C ÷ 2π = √(A ÷ π)
π ≈ 3.14159265. Example: radius 5 → C = 2 × π × 5 ≈ 31.4159; area ≈ 78.54. Units stay the same as your input (cm in → cm out; area in square units).
Frequently asked questions
What is the circumference of a 10 inch circle?
A 10-inch diameter circle has a circumference of about 31.42 inches.
About this tool
- Written by
- [Author: to be assigned]
- Reviewed by
- Formula tests passed · human review pending
- Last updated
- 31 Oct 2026
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