Circle Calculator
Every measurement of a circle can be derived from any single one of them. Enter whichever value you know — radius, diameter, circumference or area — and this calculator completes the other three.
Results
Formula
How to use this calculator
- Select which measurement you already know.
- Enter its value.
- Press Calculate to complete the full set.
Worked example
A circle with radius 7.
- Diameter: 2 × 7 = 14.
- Circumference: 2π × 7 ≈ 43.98.
- Area: π × 7² ≈ 153.94.
Result: Diameter 14, circumference ≈ 43.982, area ≈ 153.938.
Frequently asked questions
What is π and how precise is it here?
π (pi) is the constant ratio of circumference to diameter, about 3.14159. CalcMira uses JavaScript’s full double-precision π rather than the rounded 3.14.
How do I find the radius from the area?
Divide the area by π and take the square root: r = √(A ÷ π). This calculator does that automatically when you select Area.
Are the units squared for area?
Yes — if the radius is in inches, circumference is in inches and area is in square inches. Keep units consistent.
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