Perimeter Aqa Foundation

Perimeter

What is perimeter?

• Perimeter is the total distance around the outside of a 2D shape

  • The perimeter of a circle is called the circumference

• Perimeter is a length in one dimension

  • Units of measure include mm, cm, m etc

How do I find the perimeter of a 2D shape?

• Add together the lengths of all of the sides of the shape

• For any regular 2D shape, the perimeter will be the number of sides, multiplied by the length of one side

  • For example, the perimeter of a square of side length x cm will be 4x cm

How do I find the perimeter of a compound shape?

• Shapes may be made up of two or more 2D shapes, these are called compound shapes

  • Compound shapes can usually be split into rectangles, triangles and parts of circles

  • You will need to be confident with the properties of 2D shapes

    • For example, the distance between the centre point of a circle and a point on the circumference is its radius

  • Look out for sides that are equal, for example in a rectangle, parallelogram, or isosceles triangle

    • Dashes may be used to mark the equal sides, or the question may tell you which sides are equal

  • You may need to use certain formulas to calculate lengths

    • For example, you may need to use Pythagoras’ theorem to calculate a length on a right-angled triangle

  • You may need to use the given information to find the lengths of some of the sides

    • For example, the L-shape below can be split into two rectangles

    • The sum of the lengths of two shorter sides will be the same as the length of the longer side opposite