54 · Calculators

Circle Calculator

Know one measurement of a circle? Enter it to get the radius, diameter, circumference and area.

Area

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How to use the circle calculator

  1. Choose what you know: radius, diameter, circumference or area.
  2. Enter the value.
  3. Read the other measurements.

Circle formulas

  • Diameter = 2 × radius
  • Circumference = 2 × π × radius
  • Area = π × radius²

Examples

Radius 5

Area 78.539816 · circumference 31.415927

Circumference 10

Radius 1.591549

Questions

What value of π is used?

JavaScript’s full double-precision value, about 3.141592653589793.

What units are the results in?

The same units you entered: area is in those units squared.