Area and Perimeter KS2 — Year 6 Guide with Formulae

Perimeter vs Area — What’s the Difference?

Think of a garden. The perimeter is the fence that goes around the outside. The area is the grass that covers the ground inside.

Perimeter is a length — measured in cm or m. Area is a surface — measured in cm² or m². Two completely different things. If your child remembers the fence vs carpet analogy, they’ll be fine.

Perimeter

Finding the perimeter is straightforward: add up all the sides. For a rectangle there’s a handy shortcut:

Example: a rectangle is 8 cm long and 5 cm wide.

Watch out for compound shapes where some sides aren’t labelled. Children need to work out the missing lengths from the ones given. This catches a lot of kids out in SATs.

Area of Rectangles

This one’s simple:

Example: 8 cm × 5 cm = 40 cm².

The important bit: the answer must be in square units — cm², not just cm. This is a common mark dropped in SATs. The number is right but the unit is wrong.

Area of Triangles

Here’s the tricky bit that catches lots of children out: the height must be perpendicular — straight up from the base at a right angle. Not along the sloped side. In SATs diagrams, the perpendicular height is usually shown with a dashed line and a small square in the corner.

A nice way to remember: a triangle is half a rectangle. That’s why you divide by 2.

Area of Parallelograms

Same catch as triangles: use the perpendicular height, NOT the slant height. Imagine slicing off one end of the parallelogram and sticking it on the other side — you’d get a rectangle. That’s why the formula is the same as a rectangle’s (without the ÷ 2).

Compound Shapes

SATs love L-shapes, T-shapes, and other irregular shapes made from rectangles stuck together. There are two approaches:

• Split method: Divide the shape into separate rectangles. Find each area. Add them up.
• Complete-and-subtract method: Imagine the whole big rectangle, calculate its area, then subtract the missing piece.

Both methods give the same answer. Some shapes suit one method better than the other. Encourage your child to try both and see which feels easier for each question.

The key skill is working out missing side lengths. If one side of an L-shape is 10 cm and a step up is 4 cm, the remaining bit is 6 cm. This is basic subtraction, but under exam pressure it’s where marks get dropped.

SATs Questions

Area and perimeter questions in SATs usually take one of these forms:

• Given measurements, find the area or perimeter of a shape.
• Given the area, work backwards to find a missing length.
• Compare areas or perimeters of two shapes.
• Find the area of a compound shape made from rectangles.

The backwards questions are the trickiest. If the area of a rectangle is 48 cm² and the length is 8 cm, what’s the width? Divide: 48 ÷ 8 = 6 cm. Same formula, just rearranged.

Top Tip

Before your child starts calculating, they should ask themselves: “Am I finding the distance around the outside, or the space inside?” Reading the question twice takes five seconds and can save them from a silly mistake that costs real marks. Circle the word “area” or “perimeter” in the question — it keeps their brain on track.