How it works
Provide a radius, diameter, circumference, or area to calculate every main circle measurement. Inputs are calculated locally in the browser, and valid values are retained in the page URL for bookmarking.
Input query strings and outputs
Use an input name in this page’s URL as ?name=value, and join additional inputs with &. Portable shared links may instead use the compact ?ac= state parameter.
Input query strings
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?given=Known measurementChoice · Required · Default: radius · Accepted values: radius, diameter, circumference, area
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?radius=RadiusNumber · Required · Default: 10 · Used when given = radius
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?diameterInput=DiameterNumber · Required · Default: 20 · Used when given = diameter
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?circumferenceInput=CircumferenceNumber · Required · Default: 62.831853 · Used when given = circumference
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?areaInput=AreaNumber · Required · Default: 314.159265 · Used when given = area
Outputs
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radiusResultRadiusNumber · Primary output
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diameterDiameterNumber
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circumferenceCircumferenceNumber
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areaAreaNumber
Formula notes
D=2R; C=2πR; A=πR²; solve the known measurement for R, then calculate the rest.
Input guidance
Use consistent units for every length or measurement in the same calculation. Results are educational mathematical estimates and should be checked before high-stakes use.