Circle Area Calculator
Calculate the area and circumference of a circle from its radius. Enter the radius in any unit and the results use the same unit squared for area.
8 of 8 free uses remaining today
Calculate the area and circumference of a circle from its radius. Enter the radius in any unit and the results use the same unit squared for area.
Worked example
Example calculated from the starting values. Enter your own values and press Calculate to get your result.
With the default inputs (radius = 5), the results are: area 78.540; circumference 31.416; diameter 10.
Quick reference: radius vs result
Reference table based on the example values; it is not your calculation result.
| Radius | Area | Circumference | Diameter |
|---|---|---|---|
| 2.5 | 19.635 | 15.708 | 5 |
| 5 | 78.540 | 31.416 | 10 |
| 10 | 314.159 | 62.832 | 20 |
| 25 | 1,963.495 | 157.080 | 50 |
| 50 | 7,853.982 | 314.159 | 100 |
| 100 | 31,415.927 | 628.319 | 200 |
Frequently asked questions
What formula does this calculator use?
Area = pi × r^2; Circumference = 2 × pi × r; Diameter = 2 × r. Variables: r = radius.
What do I need to enter?
You need radius. Results update as you type.
What is an example result?
With the default inputs (radius = 5), the results are: area 78.540; circumference 31.416; diameter 10.
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