Area and circumference of a circle from radius or diameter.
Quick answer: Calculate circle area and circumference. Free online circle calculator using radius or diameter.
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Calculate the area and circumference of a circle from its radius. Area = πr², Circumference = 2πr.
Pi is the ratio of a circle's circumference to its diameter, approximately 3.14159.
Yes — radius = diameter ÷ 2, then apply the formulas.
Area is in square units; circumference is in linear units.
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