Measurement
What the exam tests
Measurement tests choosing suitable units and converting between them for length, mass and capacity. It also tests perimeter, area and volume in practical contexts.
Core rules
- Length: 10 mm = 1 cm, 100 cm = 1 m, 1,000 m = 1 km.
- Mass: 1,000 g = 1 kg, 1,000 kg = 1 tonne.
- Capacity: 1,000 ml = 1 litre. For water, 1 litre = 1,000 cm³.
- To change a larger unit to a smaller unit, multiply. To change a smaller unit to a larger unit, divide.
- Perimeter is the distance around a shape. Area is measured in square units; volume in cubic units.
- Rectangle: area = length × width. Perimeter = 2(length + width). Cuboid volume = length × width × height.
Worked example
A rectangular garden is 25 m long and 12 m wide. Find its perimeter and area. Perimeter = 2(25 + 12) = 2 × 37 = 74 m. Area = 25 × 12 = 300 m². The perimeter is a length, so it is in metres; the area is a surface, so it is in square metres.
Traps that cost marks
Do not mix units before calculating: change 2 m 35 cm to 235 cm first. Do not write area in metres instead of square metres. When converting, check whether the answer should be larger or smaller. Do not confuse capacity in litres with volume in cubic centimetres, and do not add the length and width only once when finding a rectangle's perimeter.