A perimeter is the total lengths of all the lines that form the outside of a shape.
The perimeter of a rectangle consists of adding the four lengths together: 5cm + 3cm + 5cm + 3cm = 16cm
The perimeter of a regular polygon is the number of sides multiplied by the length of one side. A regular hexagon with a side of length 5cm has a perimeter of 6 x 5 = 30cm.
When calculating the perimeter of a compound shape, determine the starting point for the shape and work round the shape in one direction to avoid leaving any sides out of the calculation. Put a mark on the starting corner to show where you have started from to avoid missing or double counting a length.
A square is shown below. What is the perimeter of the square?
Each side is 4cm long.
4 x 4 = 16cm
Answer: 16 cm
What is the perimeter of this shape?
| Missing length | a | = 8 - 3 | = 5 |
| Missing length | b | = 8 - 4 | = 4 |
| Add clockwise | P | = 8 + 8 + 4 + 5 + 3 + 3 |
| = 31 |
Answer: 31 cm