Circle Calculator
Calculate circle area, circumference, and diameter from radius — nothing is uploaded.
Circle calculations from radius
Enter a radius and instantly get area (πr²), circumference (2πr), and diameter (2r). All calculations use the built-in Math.PI constant for maximum precision.
Everything runs in your browser — no data is sent anywhere.
FAQ
Why use radius instead of diameter? Radius is the fundamental input for circle formulas. If you have the diameter, just halve it.