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Geometry

Circumference Calculator — Radius, Diameter or Area

Enter a circle’s radius, diameter, circumference or area in cm or cm². Calculate the other measurements, including circumference to diameter.

Formula and sources updated · Data sources · 1View algorithm, constants and default inputs (JSON)

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Circumference 62.8319cm
Results
Example

Next steps

After this result, you may want to…

Circumference (cm)

Circumference (cm)Schematic; not to scale. r · Radius (cm): 10.0000 / d · Diameter (cm): 20.0000rSchematic; not to scale.r · Radius (cm): 10.0000d · Diameter (cm): 20.0000

About this calculator

Choose the measurement you know: radius, diameter, circumference or area. Lengths use centimetres and area uses square centimetres. For example, a circumference of 20 cm gives diameter 20/π ≈ 6.3662 cm. Use C = πd = 2πr and A = πr².

Worked example

calculated with the default values below

Measurement basis Radius · Known measurement 10 cm or cm² Circumference 62.8319 cm · Diameter 20.0000 cm · Area 314.1593 cm² · Radius 10.0000 cm

Method and assumptions

Formula basis and scope

C = 2πr = πd; radius is r, d/2, C/(2π) or sqrt(A/π), according to the selected known measurement.

Ideal Euclidean shapes; use consistent length units. A diameter is twice the radius.

Data sources

Disclaimer

These calculators give general mathematical results. They suit study, planning and estimation — verify anything that feeds a graded submission, a published figure or a financial commitment.

Maintained by: CalcDelta Formula and sources updated ·

Implementation source

This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.

View algorithm, constants and default inputs (JSON)

Formula and variables

C = 2πr = πd; A = πr²; r = d/2 = C/(2π) = √(A/π)

C
Circumference
r
Radius
d
Diameter
A
Area

Choose the measurement you know: radius, diameter, circumference or area. Lengths use centimetres and area uses square centimetres. For example, a circumference of 20 cm gives diameter 20/π ≈ 6.3662 cm. Use C = πd = 2πr and A = πr².

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Frequently asked questions

How do I convert a circle’s circumference to diameter?

Choose the measurement you know: radius, diameter, circumference or area. Lengths use centimetres and area uses square centimetres. For example, a circumference of 20 cm gives diameter 20/π ≈ 6.3662 cm. Use C = πd = 2πr and A = πr².