Area & perimeter
Estimating and measuring area and perimeter
Perimeter is the total distance around the edge of a shape. Area is the amount of surface a shape covers. We can measure perimeter with a ruler and estimate area by counting squares.
Measuring perimeter
To find the perimeter, measure the length of each side and add them together. Perimeter is a length, so it uses units like millimetres (mm), centimetres (cm), metres (m) and kilometres (km). Remember: 1 cm = 10 mm, 1 m = 100 cm, 1 km = 1000 m.
Estimating area by counting squares
Place the shape on a grid of squares. Count all the whole squares that are covered. Then count any square that is more than half covered and add those too. This gives a good estimate of the area.
Units of area
Area is measured in square units: mm², cm², m² and km². Choose the unit that fits the size: a drop of water is mm², a stamp or spill is cm², a pond or room is m², and a sea is km².
Worked examples
Measuring a perimeter
- A rectangle has sides 5 cm, 3 cm, 5 cm and 3 cm.
- Add every side: 5 + 3 + 5 + 3.
Answer: The perimeter is 16 cm.
Estimating an area
- A juice spill covers 10 whole centimetre squares.
- It also covers 6 squares that are more than half covered.
- Add them: 10 + 6 = 16.
Answer: The estimated area is 16 cm².
Changing units of length
- A theme park has a perimeter of 5 km.
- 1 km = 1000 m.
- 5 × 1000 = 5000.
Answer: The perimeter is 5000 m.
Choosing a unit of area
- You want the area of a sea.
- A sea is huge, so a large square unit is needed.
Answer: Use square kilometres (km²).
Where you see this in real life
- Working out how many fence panels are needed to go around a playground (perimeter).
- Estimating the area of a juice spill or a stain by counting squares.
- Choosing whether to buy tiles measured in cm² or m² to cover a wall.
- Measuring how far it is around a stamp in millimetres.
Key words
- Perimeter
- The total distance around the edge of a 2D shape.
- Area
- The amount of surface a shape covers, measured in square units.
- Square unit
- A unit for area such as mm², cm², m² or km².
- Estimate
- A sensible close answer, found here by counting whole and part squares.