⭕ Circle Calculator
Enter any one measurement — radius, diameter, area, or circumference — and instantly calculate all the others. Uses π = 3.14159265358979…
Choose which measurement you know:
Circle Formulas
π = 3.14159265358979323846…
How to Use
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1Select Your Known ValueChoose which measurement you already know — radius, diameter, area, or circumference.
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2Enter the ValueType the numeric value into the input field. Ensure it is a positive number.
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3Click CalculateAll four measurements are computed instantly using the standard circle formulas with π.
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4Copy or Use the ResultsUse the copy button to copy all four values to your clipboard at once.
Worked Example — Radius = 5
Frequently Asked Questions
Pi (π) is the ratio of a circle's circumference to its diameter. It is an irrational number approximately equal to 3.14159265358979. It appears in every formula involving circles and spheres.
Area measures the surface enclosed by the circle (in square units), while circumference is the total length around the edge of the circle (in linear units). Area = πr², Circumference = 2πr.
The radius is the distance from the centre of the circle to any point on its edge. The diameter is the full width of the circle passing through the centre — always exactly twice the radius (d = 2r).
First find the radius: r = √(A / π). Then calculate circumference: C = 2πr. For example, area = 78.54 → r = √(78.54 / π) ≈ 5 → C = 2π × 5 ≈ 31.42.
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