Last reviewed: 25 October 2026
Area and perimeter are two of the most practical topics in upper primary Mathematics, and they are easy to mix up under exam pressure. This guide explains the difference, gives every formula a Grade 6 learner needs, and works through the kinds of questions that appear in revision papers. Area is a Measurement sub-strand in KICD’s Grade 6 Mathematics curriculum design.
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Perimeter and Area: The Difference
Perimeter is the distance all the way round the edge of a shape. It is a length, so it is measured in centimetres (cm), metres (m) or kilometres (km). Area is the amount of surface a shape covers. It is measured in square units: cm², m² or km². A simple way to remember: perimeter is the fence, area is the grass inside.
Perimeter of Common Shapes
- Any shape with straight sides: add all the sides.
- Rectangle: 2 × (length + width). A 12 m by 7 m plot has a perimeter of 2 × 19 = 38 m.
- Square: 4 × side. A square of side 9 cm has a perimeter of 36 cm.
Questions sometimes work backwards: a square garden has a perimeter of 60 m, so each side is 60 ÷ 4 = 15 m.
Area of Squares and Rectangles
Area of a rectangle = length × width. A classroom floor 8 m long and 6 m wide has an area of 48 m². Area of a square = side × side, so a square of side 9 cm covers 81 cm². To find a missing side, divide: a rectangle of area 72 cm² and length 9 cm has a width of 8 cm.
Area of a Triangle
A triangle is half of a rectangle, so its area is ½ × base × height. The height must be the perpendicular height, measured at a right angle to the base, not the sloping side. A triangle with base 10 cm and height 6 cm has an area of ½ × 10 × 6 = 30 cm². Learners often forget the half, so build the habit of writing the formula first every time.
Combined Shapes
Many exam shapes look like an L or a house. Split them into rectangles, squares and triangles, find each area, then add. For an L-shaped room, draw a line to make two rectangles, for example 6 m × 4 m = 24 m² and 3 m × 2 m = 6 m², giving 30 m² in total. For a shape with a piece cut out, find the big area and subtract the missing part.
For the perimeter of a combined shape, only count the outside edges, and work out any missing lengths from the ones given before you add.
Units and Conversions
Make sure all measurements are in the same unit before you calculate. 1 m = 100 cm, but 1 m² = 10,000 cm², because a square metre is 100 cm by 100 cm. Land is often measured in hectares and acres: 1 hectare = 10,000 m². If a question gives one side in metres and another in centimetres, convert first.
Real-Life Word Problems
- A farmer fences a rectangular shamba 40 m by 25 m. Fencing costs KSh 150 per metre. Perimeter = 130 m, so the cost is KSh 19,500.
- A floor 5 m by 4 m is covered with square tiles of side 50 cm. Each tile covers 0.25 m², the floor is 20 m², so 80 tiles are needed.
- A triangular flag has a base of 60 cm and a height of 40 cm. Its area is 1,200 cm².
Common Mistakes
- Giving area in cm instead of cm², or perimeter in cm².
- Using the sloping side of a triangle as the height.
- Adding inside lines when finding the perimeter of a combined shape.
- Mixing metres and centimetres in one calculation.
Practice Plan
Draw shapes on squared paper and count squares to check the formula, then move to exam questions. The exam countdown has free daily questions and the What to Revise report shows which topics need more time. Pair this with our fractions guide and the Grade 6 Mathematics revision papers. Full timed papers with worked answers come with the Monthly Pass (KSh 500 by M-Pesa).
Ten-minute check: try the free Grade 6 CBC Challenge. It has 10 questions, each marked on the spot with the working, and it shows which topics to practise next.