Circle Calculator

Calculate circle area, circumference, and diameter from a radius.

Circle Calculator helps you compute area, circumference, and diameter from a radius. Enter radius, review the breakdown, and use the guidance below to understand what the number means — and what it does not. What the Circle calculator does Circle Calculator is built for arithmetic, algebra, geometry, and number tools. Compute area, circumference, and diameter from a radius. You enter radius, then Simple Calculators computes the result instantly. Results use standard school and engineering formulas that run privately in your browser. How the math works Area = πr². Circumference = 2πr. Diameter = 2r. The formula: A = πr². Circumference C = 2πr.