Circle Calculator
Calculate circle area, circumference, diameter and radius from any one value. Also computes arc length and sector area.
Frequently asked questions
- Which formulas does it use?
- Area = πr², circumference = 2πr, diameter = 2r. Enter any one measurement and the rest follow.
- What are arc length and sector area?
- The curved part of the circle and the pie-slice region for a given central angle, both proportional to that angle over 360°.
- Can I start from the area?
- Yes — pick Area as the unit and the tool works backwards to the radius, then to every other measurement.
This tool runs entirely in your browser. No data is uploaded anywhere.