###### Asked in Geometry

Geometry

# What is the formula for area of a half circle but you don't have the radius?

## Answer

###### Wiki User

###### 03/20/2010

If you have the diameter, then the formula for the area of a semi-circle is:

**(pi x (diameter/2)****2****)/2**

That is,

- Divide the diameter in two to find the radius (diameter/2)
- Square the radius (radius x radius)
- Multiply it by pi (3.1416)
- Divide the answer by two to find half the circle.
- Remember your units. The answer will be in square inches, or square centimeters or square somethings.

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