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    Circle Calculator

    Calculate a circle's area, circumference, diameter and radius from any one value. Free online circle calculator with the formulas A = πr² and C = 2πr.

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    How to use Circle Calculator

    1. 1Choose what you know: radius, diameter, circumference or area
    2. 2Type the value and an optional unit
    3. 3Read all four measurements instantly and copy them

    Frequently asked questions

    How do you find the area of a circle?▾

    A = πr². A circle with a 5 cm radius has an area of π × 25 ≈ 78.54 cm².

    How do you find the circumference?▾

    C = 2πr = πd. A 5 cm radius gives about 31.42 cm.

    How do I get the diameter from the circumference?▾

    Divide by π: d = C ÷ π. A circumference of 100 cm means a diameter of about 31.83 cm.

    How do I find the radius from the area?▾

    r = √(A ÷ π). An area of 50 m² gives a radius of about 3.99 m.

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