Enter a circle's radius to calculate its diameter, circumference and area.
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Diameter is simply twice the radius. Circumference is calculated as 2π × radius, the distance around the circle. Area is calculated as π × radius², the amount of space enclosed by the circle. All three use π (pi), approximately 3.14159.
For a radius of 5: diameter = 5 × 2 = 10. Circumference = 2 × π × 5 ≈ 31.42. Area = π × 5² = π × 25 ≈ 78.54.
Entering the diameter instead of the radius, this calculator expects the radius specifically, entering a diameter by mistake will double every result.
Confusing area and circumference, circumference (2πr) is a length measured around the circle's edge, while area (πr²) is the space enclosed inside it, they use different formulas and different units (linear vs squared).
Using an overly rounded value of π for precise work, this calculator uses JavaScript's full-precision π, so results may differ slightly from hand calculations using 3.14 as an approximation.
Divide the diameter by 2 to get the radius, then enter that value.
Rearrange the formula to solve for radius first: radius = circumference ÷ (2π), or radius = √(area ÷ π), then enter that radius here.
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