# Area of a Semicircle

## Method #1 – Area from the Radius

### Formula – How to calculate the area of a semicircle from the radius

π is approximately equal to 3.1415926535

Area = (π x Radius2) ÷ 2

##### Example

A semicricle has a radius of 10 inches.

Area = (π x 102) ÷ 2

Area = (3.14159 x 100) ÷ 2

Area = 314.159 ÷ 2

Area = 157.0795 inches2

## Method #2 – Area from the Diameter

### Formula – How to calculate the area of a semicircle from the diameter

π is approximately equal to 3.1415926535

Step 1: Find the Radius from the Diameter

Radius = Diameter ÷ 2

Step 2: Find the Area from the Radius

Area = (π x Radius2) ÷ 2

### Example

A semicircle has a diameter of 20

Radius = 20 ÷ 2 = 10

Area = (π x 102) ÷ 2

Area = (3.14159 x 100) ÷ 2

Area = 314.159 ÷ 2

Area = 157.0795 inches2

## Method #3 – Area from the Circumference

### Formula – How to calculate the area of a semicircle from the circumference

π is approximately equal to 3.1415926535

Step 1: Calculate the radius from the circumference

Radius = Circumference ÷ π

Step 2: Calculate the area from the radius

Area = (π x Radius2) ÷ 2

##### Example

A semicircle has a circumference of 10

Radius = 10 ÷ π = 10 ÷ 3.14159 = 3.183102

Area = (π x 3.1831022) ÷ 2

Area = (3.14159 x 10.13214) ÷ 2

Area = 31.83103 ÷ 2

Area = 15.9155