Radius, diameter, circumference and area — enter any one.
How to use this calculator
Every field updates the result as you type — there is no submit step. The inputs below are pre-filled with a realistic example so you can see how the tool behaves before entering your own figures.
| Field | Unit | What it means |
|---|---|---|
| Known value | — | Choose one of the available options. |
| Value | — | Enter a numeric value. |
Worked example
Using the default values loaded into the calculator above, the result is:
| Input | Value |
|---|---|
| Known value | Radius |
| Value | 5 |
| Output | Value |
|---|---|
| Area | 78.53981634 |
| Radius | 5 |
| Diameter | 10 |
| Circumference | 31.41592654 |
| Sphere volume with this radius | 523.5987756 |
| Sphere surface area | 314.15926536 |
Precision and rounding
Calculations run in IEEE 754 double precision, giving about 15–17 significant decimal digits. Displayed values are rounded for readability while the full precision is retained internally, so intermediate rounding never accumulates into the final answer.
Very large or very small magnitudes switch automatically to scientific notation.
Sharing and saving a calculation
The "Copy link" button encodes every value you have entered into the page URL. Opening that link restores the calculation exactly, which makes it easy to bookmark a scenario, send it to someone else, or keep several variations side by side in separate tabs.
Frequently asked questions
What does the Circle Calculator do?
Radius, diameter, circumference and area — enter any one.
What result do the default values produce?
With the values pre-loaded in the calculator, area comes to 78.53981634.
Is this calculator free to use?
Yes. It is free, requires no account, and runs entirely in your browser — nothing you enter is transmitted or stored on a server.
Can I save or share a calculation?
Yes. The "Copy link" button builds a URL containing all your entered values. Anyone opening that link sees the same calculation.
How accurate is the result?
Calculations use double-precision floating point, accurate to roughly 15 significant digits. Displayed values are rounded for readability only.