A system built on tens
The metric system is used for measurement in Canada and almost every country in the world. Like our number system, it works in tens, which makes converting easy.
The base units
| Measures | Base unit | Symbol |
|---|---|---|
| Length | metre | m |
| Mass | gram | g |
| Capacity | litre | L |
| Time | second | s |
| Temperature | degree Celsius | °C |
Prefixes
A prefix in front of the base unit tells you how big the unit is.
| Prefix | Meaning | Length | Mass | Capacity |
|---|---|---|---|---|
| kilo– | 1,000 | kilometre (km) | kilogram (kg) | kilolitre (kL) |
| (base) | 1 | metre (m) | gram (g) | litre (L) |
| centi- | 1/100 | centimetre (cm) | — | centilitre (cL) |
| milli– | 1/1,000 | millimetre (mm) | milligram (mg) | millilitre (mL) |
Learn the prefixes once and they work for every kind of measurement.
Key relationships
- 1 km = 1,000 m
- 1 m = 100 cm = 1,000 mm
- 1 cm = 10 mm
- 1 kg = 1,000 g
- 1 L = 1,000 mL
Benchmarks: how big is it?
| Unit | About the size of |
|---|---|
| 1 mm | the thickness of a credit card |
| 1 cm | the width of your fingernail |
| 1 m | a big step, or the height of a doorknob |
| 1 km | about 12 minutes of walking |
| 1 g | a paper clip |
| 1 kg | a litre of water, or a bag of sugar |
| 1 mL | a few drops; about 20 drops of water |
| 1 L | a large milk carton |
Choosing the right unit
Pick a unit that gives a sensible number:
- Length of a pencil → cm
- Distance to another city → km
- Mass of an apple → g
- Mass of a person → kg
- Water in a bathtub → L
- Medicine dose → mL
Converting
To go to a smaller unit, multiply. To go to a bigger unit, divide.
- 3 m = 3 × 100 = 300 cm
- 4,500 g = 4,500 ÷ 1,000 = 4.5 kg
Worked examples
Example 1: How many centimetres in 2.5 m?
2.5 × 100 = 250 cm.
Example 2: Which unit would you use for the mass of a car?
Kilograms (a car is about 1,500 kg).
Example 3: 750 mL is how many litres?
750 ÷ 1,000 = 0.75 L.
Common mistakes
- Multiplying when you should divide. Going to a bigger unit makes the number smaller.
- Mixing up centi- and milli-.
- Using an unsuitable unit, like measuring a road in millimetres.
Try it yourself
- How many metres in 4 km?
- How many millilitres in 2 L?
- Convert 60 mm to cm.
- Which unit for the length of a soccer field?
Answers: 1) 4,000 m 2) 2,000 mL 3) 6 cm 4) metres
Quick recap
- The metric system uses base units metre, gram and litre.
- Prefixes like kilo-, centi- and milli– tell the size.
- Multiply to go to a smaller unit; divide to go to a bigger one.