What is perimeter?
Perimeter is the total distance around the outside of a shape. To find it, add up the lengths of all the sides.
- A rectangle with sides 4 units and 2 units → 4 + 2 + 4 + 2 = 12 units
Perimeter is measured in units (not square units). Think of walking around the outside edge of the shape.
How to identify perimeter on a grid
On a grid, each square usually represents one unit. To find perimeter, count the number of unit lengths around the shape.
- Trace around the outside of the shape.
- Count each unit side you pass.
- Add all sides together for the total perimeter.
Be careful not to count any inside lines—only the outer edges count toward the perimeter.
Examples on grids
Look at how perimeter is found by counting units around shapes placed on a grid.
- A square covering 3 units by 3 units → 3 + 3 + 3 + 3 = 12 units
- A rectangle covering 5 units by 2 units → 5 + 2 + 5 + 2 = 14 units
If a side is longer than one unit, count carefully to include each unit along that side.
Helpful tips when finding perimeter
Use these strategies to avoid mistakes while finding perimeter on grids.
- Always start at one corner and go all the way around.
- Mark the sides as you count to keep track.
- Double-check your addition after counting all the units.
Perimeter measures the boundary. It is different from area, which measures space inside a shape.