Which unit should I use?
| Measuring | Small things | Medium things | Big things |
|---|---|---|---|
| Length (how long, tall, far) | mm: an ant | cm: a pencil · m: a garden | km: between two towns |
| Weight (how heavy) | g: an apple, a letter | kg: a schoolbag, a person | tonnes: a lorry, a ship’s container |
| Capacity (how much a container holds) | ml: a spoon, a cup | l: a bucket, a bath, a swimming pool |
Converting between units
| Length | Weight | Capacity |
|---|---|---|
| 10 mm = 1 cm | 1000 g = 1 kg | 1000 ml = 1 l |
| 100 cm = 1 m | 1000 kg = 1 tonne | |
| 1000 m = 1 km |
Memory hook: kilo means 1000: a kilogram is 1000 grams, a kilometre is 1000 metres. Centi means hundredth: there are 100 centimetres in a metre, like 100 years in a century.
- Big unit → small unit: multiply (you’ll need more of the smaller ones). 3 kg = 3 × 1000 = 3000 g
- Small unit → big unit: divide. 250 cm = 250 ÷ 100 = 2.5 m
Decimals
| 1.2 m = 120 cm | 0.9 km = 900 m | 0.8 kg = 800 g |
| 1.5 l = 1500 ml | 0.25 l = 250 ml | 2.05 kg = 2050 g |
Comparing
Always change to the same unit first.
Which is longer: 850 m or 0.9 km? → 0.9 km = 900 m → 0.9 km is longer, by 50 m.
Watch out! 1.2 m is not 12 cm, and it’s not 1 m 2 cm. 1.2 m = 1 m 20 cm = 120 cm.
Top tip: in a “how much more” question, give your answer in the unit the question asks for. Convert first, then subtract.
🗂️ Length, weight or capacity?1 of 8
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🎮 Convert and compareQuestion 1 of 5
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