Circle Calculator
Area, circumference, and diameter from a radius
Use this when you need a fast, accurate result — no sign-up, works entirely in your browser.
Radius—
Diameter—
Circumference—
Area—
How to Use
- Enter your details into the fields above.
- Click the calculate button to get your result instantly.
- Use the clear button to start a new calculation.
Example
- Radius 5 → Area ≈ 78.54; circumference ≈ 31.42; diameter 10
- Diameter = 16 → Radius 8, circumference ≈ 50.27, area ≈ 201.06
Formula
Area = πr². Circumference = 2πr. Diameter = 2r. The diameter is always twice the radius regardless of the unit system.
About Circle Calculator
Area, circumference, and diameter from a radius. This free online tool gives you fast, accurate results without registration or downloads.
Everything runs locally in your browser, so your data is never uploaded or stored — privacy first.
Frequently Asked Questions
Is this tool free to use? +
Yes, it is completely free with no registration or download required.
Is my data private? +
Yes. Everything is processed locally in your browser. Nothing is uploaded or stored on our servers.
Does it work on mobile? +
Yes, it works on any device — phone, tablet, or desktop.