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Circle Diameter, Area & Circumference Calculator

The Circle Diameter, Area, & Circumference Calculator is a user-friendly tool designed to quickly and accurately calculate the area of a circle, the diameter of a circle, or the circumference of a circle. The calculator is useful for students and professionals who need to perform these calculations for various applications, such as geometry, engineering, or physics.  The user can enter the diameter, circumference, or area of the circle, and the calculator will solve for the remaining two parameters.  The calculator is easy to use and requires no advanced mathematical skills or knowledge.


  1. Select US or Metric Units

  2. Select Input type:

    • Diameter​

    • Circumference

    • Area

  3. Enter Input value

  4. Select the units for the input value.

  5. Click the Calculate button

  6. The results are displayed in the Results table


Equations for the circumference and area of a circle

Area = pi x D^2 /4

Circumference = pi x D

where:     D= diameter

Cir Dia Area Circumference
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