📖Definition
The Perimeter of a 2D shape is the length of its outline.
Method
Most of the time you just need to find the length of each side of the shape and add them all up.
Some shapes have formulas for their perimeters:
Perimeter of a square with sides a = 4a
Perimeter of a rectangle with sides a, b = 2(a + b)
💡Tips/hints
For more complex shapes, be sure to include the length of every side when calculating the perimeter. It might help to mark the sides as you go around the shape.
✏️Example
Calculate the perimeter of the shape below.
Diagram
✅Solution
First, work out the lengths of the sides that aren't marked.
The long vertical = 2.5m + 2.5m = 5m
The short horizontal = 4.5m - 2m = 2.5m
So, starting at the top left hand corner and going round clockwise
Perimeter = 2 + 2.5 + 2.5 + 2.5 + 4.5 + 5 = 19m