5.1 Units of Measure


2026 📋 Syllabus Objectives

By the end of this topic, you should be able to:

  1. Use metric units of mass, length, area, volume, and capacity in practical situations, and convert quantities into larger or smaller units.
  2. Know and use the following units: mm, cm, m, km (length) | mm², cm², m², km² (area) | mm³, cm³, m³ (volume) | ml, l (capacity) | g, kg (mass) — and convert between them, including between area units (e.g. cm² ↔ m²) and between volume and capacity units (e.g. m³ ↔ litres).

1. What Are Metric Units?

The metric system is the standard system of measurement used in science and in most countries around the world. Every unit in the metric system is based on powers of 10 (10, 100, 1000…), which makes converting between units straightforward — you only ever multiply or divide by these numbers.

There are five main types of measurement you need to know for this topic:

TypeWhat it measuresUnits you need to know
LengthHow long or far something ismm, cm, m, km
AreaThe amount of flat surface something coversmm², cm², m², km²
VolumeThe amount of 3D space something takes upmm³, cm³, m³
CapacityHow much liquid a container can holdml, l (litres)
MassHow heavy something isg, kg

2. Length Units

Length tells us how long, tall, or wide something is.

The units in order from smallest to largest are:

mm → cm → m → km (millimetres → centimetres → metres → kilometres)

Here are the key conversion facts you must memorise:

  • 10 mm = 1 cm (there are 10 millimetres in 1 centimetre)
  • 100 cm = 1 m (there are 100 centimetres in 1 metre)
  • 1000 m = 1 km (there are 1000 metres in 1 kilometre)

You can picture this as a number line going left to right:

mm ——(÷10)——▶ cm ——(÷100)——▶ m ——(÷1000)——▶ km
mm ◀——(×10)—— cm ◀——(×100)—— m ◀——(×1000)—— km

3. Mass Units

Mass tells us how heavy an object is.

The units you need are:

g → kg (grams → kilograms)

Key conversion fact:

  • 1000 g = 1 kg (there are 1000 grams in 1 kilogram)
g ——(÷1000)——▶ kg
g ◀——(×1000)—— kg

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