Circle Calculator
Calculate a circle's area, circumference, diameter and radius from any one of them.
Result
Area
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Enter a value greater than zero.
Choose which measurement you know — radius, diameter, circumference or area — enter its value, and we'll work out the rest.
Frequently asked questions
What is the formula for the area of a circle?
Area = π × r², where r is the radius. For example, a circle with radius 5 has an area of π × 25 ≈ 78.54 square units.