Method #1 – Area from Radius
Calculators
Formula – How to calculate the area of a circle using the radius
π is approximately 3.1415926535
Area = π x Radius2
Example
A circle has a radius of 10
Area = π x 102 = 3.14159 x 102 = 3.14159 x 100 = 314.59
Method #2 – Area from Diameter
Calculator
Formula – How to calculate the area of a circle using the diameter
π is approximately 3.1415926535
Area = 2 x π x Radius2
Example
A circle has a diameter of 10
Area = 2 x π x 102 = 2 x 3.14159 x 102 = 2 x 3.14159 x 100 = 628.318
Method #3 – Area from Circumference
Calculator
Formula – How to calculate the area of a circle using the circumference
π is approximately 3.1415926535
Area = π x (Circumference ÷ π ÷ 2)2
Example
A circle has a circumference of 10
Area = π x (10 ÷ π ÷ 2)2
Area = 3.14159 x (10 ÷ 3.14159 ÷ 2)2
Area = 3.14159 x (1.59155)2
Area = 3.14159 x 2.5330
Area = 7.5976