Circle Calculator
Calculate circle instantly in your browser.
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What this tool does
Calculate circle instantly in your browser. Uses full-precision π; a radius of 5 gives an area of about 78.5398.
How to use the Circle Calculator
- Enter or select given.
- Enter or select value of the given measurement.
- Read the calculated result; change any measurement to compare alternatives.
Formula
r, d, C and A are all linked through π: d = 2r, C = 2πr and A = πr² — so any one measurement determines the other three.
- given
- Given
- value
- Value of the given measurement
Uses full-precision π; a radius of 5 gives an area of about 78.5398.
Worked example
For circle calculator, the following measurements illustrate the exact method: Given: radius; Value of the given measurement: 5.
Inputs
- GivenRadius
- Value of the given measurement5
Result
- Radius5
- Diameter10
- Circumference31.42
- Area78.54
Results explained
- Radius
- Radius from the formula above. Uses full-precision π; a radius of 5 gives an area of about 78.5398.
- Diameter
- Diameter from the formula above. Uses full-precision π; a radius of 5 gives an area of about 78.5398.
- Circumference
- Circumference from the formula above. Uses full-precision π; a radius of 5 gives an area of about 78.5398.
- Area
- Area from the formula above. Uses full-precision π; a radius of 5 gives an area of about 78.5398.
Frequently asked questions
r, d, C and A are all linked through π: d = 2r, C = 2πr and A = πr² — so any one measurement determines the other three.
Uses full-precision π; a radius of 5 gives an area of about 78.5398.
Where mathematically meaningful, yes. Fields specify permitted ranges and undefined operations display an error.
Exact integer calculations use safe integers; decimal calculations use browser floating point, so small rounding differences can occur.
All values remain in your browser and are never uploaded.