Video and Examples
Finding the area of circles using the formula π • r • r
The area of any shape is the number of square units inside that shape. In the figure to the left, the square has an area of 36 square units, because there are 36 units inside the square. If each unit square in the circle were counted (including all the partial squares), there would be 28.26 unit squares inside the circle, so the area of this circle would be 28.26 square units. However, it is easier to use the following formula:
where A represents the area, and r is the radius of the circle.
Finding area using π = 22/7
Finding area using π = 3.14





In terms of π.

Use this applet to observe how to find the area of any circle using either or and when given the radius or the diameter. 
Selfcheck
Q1: What is the area of a circle with a radius of 10cm? (Use π = 3.14) [show answer]
Q2: What is the area of a circle with a radius of 7cm? (Use π = 3 1/7) [show answer]
Q3: What is the area of a circle with a radius of 3cm in terms of π? [show answer]