# Area of a Circle Calculator

Use this calculator to easily calculate the area of a circle, given its radius in any metric: mm, cm, meters, km, inches, feet, yards, miles, etc.

### Calculation results

28.274334 cm2 Circle area
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## Area of a circle formula

The formula for the area of a circle is π x radius2, but the diameter of the circle is d = 2 x r2, so another way to write it is π x (diameter / 2)2. Visual on the figure below: π is, of course, the famous mathematical constant, equal to about 3.14159, which was originally defined as the ratio of a circle's circumference to its diameter. The formula above is the one used in our area of a circle calculator.

## How to calculate the area of a circle?

Calculation is easy once you have measured the circle's radius or diameter, or if you know it from plans and schematics: just plug the numbers into the formulas above use our area of a circle calculator above. If you are measuring it by hand, remember that the diameter is the largest measurement you can get from a circle.