Learn how how to find the Area and Circumference of Circles when you have the radius or the diameter of the circle.
Step by step guide to solve Circles
- In a circle, variable \(r\) is usually used for the radius and \(d\) for diameter and \(π\) is about \(3.14\).
- Area of a circle \(=πr^2\)
- Circumference of a circle \(=2πr\)
Example 1:
Find the area of the circle. 
Solution:
Use area formula: Area \(=πr^2\),
\(r=6\) \(in\), then: Area \(=π(6)^2=36π, π=3.14\) then: Area \(=36×3.14=113.04\) \(in^2\)
Example 2:
Find the Circumference of the circle. 
Solution:
Use Circumference formula: Circumference \(=2πr \)
\(r=9 \) \(cm\) , then: Circumference \(=2π(9)=18π \)
\(π=3.14\) then: Circumference \(=18×3.14=56.52\) \(cm\)
Example 3:
Find the area of the circle. 
Solution:
Use area formula: Area \(=πr^2\),
\(r=6\) \(in\), then: Area \(=π(4)^2=16π, π=3.14\) then: Area \(=16×3.14=50.24\) \(in^2\)
Example 4:
Find the Circumference of the circle. 
Solution:
Use Circumference formula: Circumference \(=2πr \)
\(r=9 \) \(cm\) , then: Circumference \(=2π(6)=12π \)
\(π=3.14\) then: Circumference \(=12×3.14=37.68\) \(cm\)
Exercises
Find the area and circumference of each circle. \((\pi=3.14)\)
Download Circles Worksheet
- \(\color{blue}{Area: \ 50.24 \ in^2 , \ Circumference: \ 25.12 \ in}\)
- \(\color{blue}{Area: \ 1,017.36 \ cm^2, \ Circumference: \ 113.04 \ cm}\)
- \(\color{blue}{Area: \ 78.5 \ m^2, \ Circumference: \ 31.4 \ m}\)
- \(\color{blue}{Area: \ 379.94 \ cm^2 , \ Circumference: \ 69.08 \ cm}\)
