Circle Calculator
Radius, diameter, circumference, area — enter any one.
Show Work
Formulas
About the Circle Calculator
The Circle Calculator is a free tool for everyday maths and number work. It runs right in your web browser, so there is nothing to download. Radius, diameter, circumference, area — enter any one.
How it works
Type your numbers into the boxes. The answer shows up right away — you do not have to press a button. If you change a number, the answer changes too. So you can try different numbers and watch what happens, or check an answer you worked out yourself. Just make sure each box has the right kind of number in it.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
How do I use the Circle Calculator?
Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.
Is it free? Does it work without internet?
Yes to both. It is free with no sign-up, and once the page has loaded it keeps working even with no internet.
Where does my data go?
Nowhere — every calculation runs on your own device. Nothing you enter is uploaded, logged, or stored.
Common Use Cases
Check your work
Worked it out yourself? Use the Circle Calculator to make sure your answer is right.
Learn while you do it
Seeing what you put in and what comes out helps you understand how they fit together.
Get an answer fast
Type what you have and get the answer in seconds — on a phone, tablet, or computer.
Safe and private
Everything you type stays on your device. Nothing is sent to a server or saved.
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