Primary 4 · Measurement & Geometry
P4 area and perimeter
In P4, your child finds the missing side of a rectangle or square from its area or perimeter. Then come composite figures, L and U shapes made of rectangles. Area splits the shape into pieces. Perimeter traces the outside once, and mixing the two up is where the marks go.
- Taught in
- Term 4
- Syllabus
- 3 skills
- Usual slip
- Adds the rectangles' perimeters
What your child learns in P4 area and perimeter
Three skills, each with what it looks like on a worksheet.
See the syllabus wording
- finding one dimension of a rectangle given the other dimension and its area/perimeter
- finding the length of one side of a square given its area/perimeter
- finding the area and perimeter of composite figures made up of rectangles and squares
Find a missing side of a rectangle
From the perimeter: halve it to get the length and the breadth together, then take away the side you know. From the area: divide it by the side you know.
Find the side of a square
A square's four sides are equal. A perimeter of 32 cm gives a side of 32 ÷ 4 = 8 cm. An area of 64 cm² also gives a side of 8 cm, because 8 × 8 = 64.
Area and perimeter of composite figures
A composite figure is made of rectangles and squares joined together. For the area, split it into rectangles and add them. For the perimeter, trace the outside once, working out any side with no label.
Key facts and formulas
- The breadth from the areaExamplebreadth →
- The length from the perimeterExamplelength →
- The side from the perimeterExampleside →
- The side from the areaExample side →
- Composite figuresArea: split into rectangles, then add. Perimeter: the outside edge only.area → perimeter →
Words to know
- Perimeter
- The distance all the way round the outside of a shape.
- Area
- The space a flat shape covers, measured in square units such as cm².
- Composite figure
- A shape made by joining rectangles and squares, like an L or a U.
- Breadth
- The other side of a rectangle, beside its length. Area is length × breadth.
- Missing side
- A side with no label, worked out from the sides that are labelled.
The sentence that costs the mark
An L-shaped figure has all six of its sides marked. What is its perimeter, the distance all the way round?
What the working usually does
splitsthe L-shape=52 cm
Splits it into two rectangles and adds both perimeters. That is right for the AREA, so it feels right here, but it counts the join edge twice.
What the question asked
tracesthe L-shape=42 cm
Traces the outside boundary once, adding only the outer sides. The edge where you would cut is not part of the outside at all.
Splitting into rectangles is the correct move for the area, so a child reuses it here and both totals look tidy. Only running a finger round the outside shows the join edge should never have been counted.
The same P4 area and perimeter question, worked properly
Lah works through it the way she does every question in StudyLah: one step at a time, marking the picture as she goes.
The figure below is formed from 3 rectangles. Find its perimeter.
- The perimeter is the distance all the way round the outside. Do not add up the three rectangles' perimeters, because the lines where they join are inside the figure.
- The long side runs across all three pieces: 3 + 8 + 5 = 16 cm.
- Each outer side is the long piece and a leg together: 3 + 6 = 9 cm.
- The two inner sides of the gap are 6 cm each, as long as a leg. Add all eight sides: 16 + 9 + 5 + 6 + 8 + 6 + 3 + 9 = 62 cm.
- So the perimeter of the figure is 62 cm.
Every question in StudyLah comes with a walkthrough like this one.
Try it freeThree quick P4 area and perimeter questions
Try them together, then tap to check.
Question 1
A rectangular field has a breadth of 12 cm and a perimeter of 84 cm. Find its length.
Show answer
Answer30 cm. The length and breadth together are half the perimeter, 84 ÷ 2 = 42 cm, so the length is 42 − 12 = 30 cm.
Question 2
The area of a square is 81 cm². What is the length of one side?
Show answer
Answer9 cm. The side times itself gives the area, and 9 × 9 = 81.
Question 3
The figure is made up of Square A of side 8 cm and Rectangle B of breadth 7 cm. Find the area of Rectangle B.
Show answer
Answer91 cm². B is 5 cm taller than A, so its length is 8 + 5 = 13 cm, and its area is 13 × 7 = 91 cm².
Helping at home
How to tell it has clicked
Ask your child to trace the perimeter with a finger while you watch. If the finger stays on the outside the whole way and never cuts across the middle, they have it.
A quick question also works: "does the perimeter go along the dashed line?" The answer is no, and a child who can say why (it is inside, not around) has understood it.
Try this tonight
Walk the outline of a room that has an alcove, keeping one hand on the wall the whole way. Your hand never crosses the middle of the room. That path is the perimeter. Splitting the room into rectangles is for the floor space, the area, a different job.
Then draw an L on paper and find both: the area by splitting and adding, the perimeter by tracing round once. Doing them side by side makes the difference stick.
Before and after P4 area and perimeter
Builds on
Primary 3 Area and PerimeterMeasures around a shape and inside it
Builds on
Primary 4 Rectangles and SquaresKnows which sides and corners must match
You are here
Primary 4 Area and Perimeter
Splits for area, traces for perimeter
Leads to
Primary 5 Area of TriangleHalves base times perpendicular height
Leads to
Primary 5 Volume of Cube and CuboidBuilds cuboids from unit cubes
Leads to
Primary 6 CirclesFinds the area and perimeter of circles
In the PSLE's hardest questions
More in Primary 4
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See how your child is doing on this topic
StudyLah marks each step separately, so you can see whether it was the setup or the arithmetic that cost the mark.