Free Maths Calculator

Circle Calculator

Start from any one circle measurement, the radius, diameter, circumference or area, and get all four, with the working shown in both exact pi form and rounded decimals. Built for the circle questions at GCSE where the given value is rarely the one the formula wants.

Try It: Enter Your Numbers

Your question

Updates as you type

Answer

Method, Step by Step

    Worked Example

    A circle has a radius of 5 cm. Find its circumference and area.

    1. Circumference = 2πr = 2 × π × 5 = 10π ≈ 31.42 cm
    2. Area = πr² = π × 5² = 25π ≈ 78.54 cm²

    Answer: Circumference 10π cm, area 25π cm²

    Try These Yourself

    A circle has diameter 12 cm. What is its circumference, in terms of π?Show answerHide answer

    Answer: 12π cm

    C = πd = 12π.

    A circle has area 36π cm². What is its radius?Show answerHide answer

    Answer: 6 cm

    r² = 36, so r = 6.

    A circle has circumference 20π cm. What is its area, in terms of π?Show answerHide answer

    Answer: 100π cm²

    2r = 20 so r = 10, then area = π × 10².