Calculyn

Circle Calculator

Get a circle's area, circumference and diameter from its radius.

Results update as you type.

Area

78.5398square units
Circumference
31.4159
Diameter
10
Area78.5398

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How it works

Every circle measurement comes from the radius and π (about 3.14159). Area grows with the square of the radius.

Formula

Area = πr² · Circumference = 2πr · Diameter = 2r

Example

A circle with radius 5 has area 78.5398, circumference 31.4159 and diameter 10.

Assumptions & limitations

  • Results are rounded for display.

Frequently asked questions

I only know the diameter.

Divide it by 2 to get the radius, then enter that.