Perimeter
Total distance around a shape.
Key idea
Total distance around a shape.
In depth
Perimeter is the total distance around a shape, found by adding all side lengths. It is a length, measured in units like cm, not square units.
Worked example
A rectangle 7 by 3 has perimeter 2(7 + 3) = 20.
Formula
Real-world uses
- Calculating how much fencing or skirting board is needed
- The length of a running track lap
Common mistake
Mixing perimeter with area, or forgetting to include all sides.
How to learn this
- Read the key idea and say it in your own words.
- Work through the worked example, then try a similar problem.
- Use the interactive lesson’s visual and mini-quiz to check the pattern.
Frequently asked questions
What is Perimeter?
Total distance around a shape. It is a topic at the beginner level in Geometry.
What is the formula for Perimeter?
The key formula is P = sum of sides.
Where is Perimeter used in real life?
Real-world examples: Calculating how much fencing or skirting board is needed; The length of a running track lap.
What should I learn before Perimeter?
Make sure you are comfortable with Special Right Triangles, the previous topic in Geometry.
What is a common mistake with Perimeter?
Mixing perimeter with area, or forgetting to include all sides.
How can I practise Perimeter?
Open the interactive lesson, play with the visual, then answer the three-question mini-quiz. Getting two right marks the topic complete.
What comes after Perimeter?
Move on to Area of Rectangle and Square next.
Related beginner topics in Geometry
- Points, Lines and Planes – The undefined building blocks of geometry.
- Line Segments and Rays – A segment has two endpoints; a ray starts at a point and goes on forever.
- Angles – Two rays sharing an endpoint; measured in degrees.
- Types of Angles – Acute <90°, right 90°, obtuse between 90° and 180°, straight 180°.
- Measuring Angles with a Protractor – Align the baseline and read the scale.
- Complementary and Supplementary – Pairs summing to 90° or 180°.