Circles: Area & Circumference

Interactive Tutorial • Practice Problems • Speed Quiz

Circles: Key Concepts 🟡

Circles have unique properties. The **circumference** is the distance around the circle (like the perimeter of a square), and the **area** is the space inside the circle.

  The **radius (r)** is the distance from the center to any point on the edge. The **diameter (d)** is the distance across the circle through the center.   $$d = 2r$$

  **Pi ($\pi$)** is a special number, approximately **3.14159**, which represents the ratio of a circle's circumference to its diameter.

 
Score: 0
 
Streak: 0

Video: The Formulas! 📐

Watch this video to visualize the formulas for a circle's area and circumference.

 
 
 

Practice Problems

Calculate the circumference or area for each problem. Use 3.14 for $\pi$ and round your answer to two decimal places.

 
   
1) Circumference with radius 5.
   

$$C = 2 \pi r$$

       
   
 
 
   
2) Area with radius 4.
   

$$A = \pi r^2$$

       
   
 
 
   
3) Circumference with diameter 10.
   

$$C = \pi d$$

       
   
 
 
   
4) Area with diameter 8.
   

$$A = \pi r^2$$

       
   
 

⚡ Circles Speed Quiz

       
Time: 0
 
Correct: 0
 
Press Start
 
           
 

Download CSV Log

Track all practice & quiz answers in a CSV file.