Circle Calculator

Calculate radius, diameter, circumference, and area from any one value. Includes arc length and sector area calculations.

Enter radius

Enter a positive number.

Enter a positive value above to see all circle measurements.

Formulae

Circumference C = 2πr = πd

Area A = πr²

Arc Length L = rθ (angle in radians)

Sector Area A = r²θ / 2 (angle in radians)

1

Enter any measurement

Type a value for radius, diameter, circumference, or area. All other values are calculated instantly.
2

Calculate arc and sector

Enter a central angle to get arc length and sector area.
3

View the diagram

An SVG circle diagram highlights the relevant measurement.

Which value do I need to enter?

Any one of radius, diameter, circumference, or area. All others are derived automatically.

How is arc length calculated?

Arc length = radius x angle (in radians). Enter the angle in degrees and it is converted automatically.

Is my data sent anywhere?

No. All calculations run in your browser.

Enter any one circle measurement — radius, diameter, circumference,

or area — and instantly get all others. An arc and sector section

calculates arc length and sector area from a central angle. Results

show both exact (with pi) and decimal forms. An SVG diagram highlights

the active measurement. All processing runs in your browser.

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