Formula and calculation method
Diameter = 2r. Circumference = 2πr. Area = πr².
Use consistent units for all comparable inputs. The displayed result is rounded; arithmetic is performed with the full available numeric precision. Check your source measurements before relying on the result.
How to use circle calculator
- Set Radius. The example below uses 5.
- Select Calculate to update the result. Reset restores the illustrated inputs. Copy, print or download your own result if you need a record.
Worked example
Example inputs
- Radius
- 5
- Diameter
- 10
- Circumference
- 31.41592654
- Area
- 78.53981634
Factors affecting your result
Use consistent units for all comparable inputs. The displayed result is rounded; arithmetic is performed with the full available numeric precision. Check your source measurements before relying on the result.
Changing radius changes the scenario being evaluated. Adjust one input at a time when comparing results, keep a copy of the assumptions, and compare values using the same unit and period. A precise arithmetic result does not make an uncertain assumption precise.
Frequently asked questions
How does the circle calculator work?
Diameter = 2r. Circumference = 2πr. Area = πr².
What inputs does Circle Calculator need?
Enter radius. Choose values that correspond to the same situation and measurement convention.
How should I interpret the circle calculator result?
Use consistent units for all comparable inputs. The displayed result is rounded; arithmetic is performed with the full available numeric precision. Check your source measurements before relying on the result.
Are my circle calculator inputs uploaded?
No. The calculation runs in this browser. Favorites, recent tool names, theme and formatting preferences may be saved locally, but calculation inputs are not sent to a calculation server or stored by this website. Shared links do not include entered values.
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