Circle Calculator
Calculate the radius, diameter, circumference and area of a circle.
Whether you're checking a geometry homework answer or estimating material for a circular surface, Lilu Baba's Circle Calculator computes diameter, circumference and area from a single radius input, instantly.
How to use this calculator
- Enter the radius of the circle.
- Area, diameter and circumference update instantly.
- Use consistent units — results are in the same linear unit (or its square, for area).
Area
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Diameter
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Circumference
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FAQ
Circle Calculator — frequently asked questions
Area = π × r², where r is the radius.
Circumference = 2 × π × r, where r is the radius.