Circle Calculator

Enter a radius to get a circle's area, circumference and diameter instantly.

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What is the Circle Calculator?

A circle calculator works out a circle's key measurements — area, circumference and diameter — from its radius, using the constant π.

How to Calculate

Area = π × r², circumference = 2 × π × r, and diameter = 2 × r.

Formula

Area = πr²   Circumference = 2πr

How to Use

  1. Enter your details in the fields above.
  2. The result updates instantly as you type.
  3. Use Copy, Print or Download PDF to save your result.

Frequently Asked Questions

What value of u03c0 is used?
The calculator uses the full precision of u03c0 (about 3.14159265u2026) for accurate results.
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