Calculate any property of a circle — radius, diameter, circumference, and area — from any single known value. Includes chord length, arc length, and sector calculations.
Enter Any One Value
SECTOR / ARC (optional)
Area
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Radius (r)
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Diameter (d)
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Circumference (C)
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Area (A)
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Enter any one circle property
All other properties calculated instantly. Optionally add an angle for sector/arc.
Frequently Asked Questions
What is the relationship between radius, diameter, and circumference?
Diameter = 2 × radius. Circumference = π × diameter = 2πr. Area = π × r². These four properties all relate through π (≈3.14159265…).
What is a sector?
A sector is a "pie slice" of a circle bounded by two radii and an arc. Sector area = (θ/360°) × πr². Arc length = (θ/360°) × 2πr, where θ is the central angle in degrees.