How Area Changes with Diameter

diameter second pizza

14

12-inch pizza		14-inch pizza

The percentage change in radius is

16.7%

The percentage change in area is

36.1%

It is easy to believe that when you change one dimension of a figure, its area changes by the same percentage. However, this is incorrect.

The area of a circle changes with the square of its diameter. For example, doubling the diameter quadruples the area. Another example: tripling the diameter makes the area go up by a factor of nine.