Circle Calculator
Fill in the value and the answer updates as you type.
How the Circle Calculator works
Area = π × r². Circumference = 2 × π × r.
Inputs and results
The Circle Calculator takes 1 input and gives 3 results.
What you enter
- Radius — starts at 5.
What you get
- Area
- Circumference
- Diameter
Example: Circle Calculator with the starting values
With radius 5, the calculator returns:
| Area | 78.5398 |
|---|---|
| Circumference | 31.4159 |
| Diameter | 10 |
Change any value above and the results update straight away.
Circle Calculator FAQ
How do I use the Circle Calculator?
Enter radius in the fields, then read area, circumference and diameter in the result panel. The answer updates as you type, and you can press Calculate or Enter to refresh it. Use “Copy link” to share your exact numbers with someone else.
What does the Circle Calculator calculate?
Area, circumference, and diameter from the radius. It returns area, circumference and diameter from the 1 value you provide.
What values does the Circle Calculator start with?
It opens with radius 5 so you can see a working result straight away. Replace them with your own numbers, or press Reset to return to these starting values.
Is the Circle Calculator free and private?
Yes. It is free, needs no account, and runs in your browser, so nothing you type is sent to or stored on our servers. See the Privacy Policy for details.
Can I rely on the Circle Calculator for important decisions?
Treat the result as a well-rounded estimate. Real situations often have details a general calculator cannot know, so confirm important decisions with a qualified professional. See the Disclaimer for more.