What Is Perimeter?
Perimeter is the total distance around the outside of a shape. If you walked along the edges of a rectangle and came back to where you started, the distance you walked is the perimeter.
How to find perimeter
Add up all the side lengths.
A rectangle with length 8 and width 5: Perimeter = 8 + 5 + 8 + 5 = 26 units
Or use the formula: P = 2l + 2w = 2(8) + 2(5) = 26
A triangle with sides 3, 4, and 5: Perimeter = 3 + 4 + 5 = 12 units
A square with side 6: Perimeter = 4 × 6 = 24 units
Perimeter vs. area
These are commonly confused:
| Perimeter | Area | |
|---|---|---|
| Measures | Distance around | Space inside |
| Units | Linear (cm, feet) | Square (cm², ft²) |
| Formula (rectangle) | 2l + 2w | l × w |
| Real-world analogy | Fence around a yard | Grass covering the yard |
A rectangle 10 × 1 has perimeter 22 and area 10. A rectangle 4 × 6 has perimeter 20 and area 24. Notice: larger perimeter does not mean larger area.
When perimeter is used
- Fencing around a yard
- Border or frame around a picture
- Ribbon around a gift box
- Track distance around a field
Related concepts
- Area and perimeter teaching guide
- Measurement: perimeter requires length measurement
- Addition: perimeter is a sum of side lengths