Standard units of measure
This topic recaps every unit of measure you need at GCSE — and the conversions between them.
Length
| Smaller → Larger | Conversion |
|---|---|
| mm → cm | ÷ 10 |
| cm → m | ÷ 100 |
| m → km | ÷ 1000 |
So 1 km = 1000 m = 100 000 cm = 1 000 000 mm.
Mass / weight
| mg → g | ÷ 1000 |
| g → kg | ÷ 1000 |
| kg → tonne | ÷ 1000 |
Capacity
| ml → cl | ÷ 10 |
| cl → litre | ÷ 100 |
| ml → litre | ÷ 1000 |
Note: 1 ml = 1 cm³, and 1 litre = 1000 cm³ = 1000 ml.
Area
| mm² → cm² | ÷ 100 |
| cm² → m² | ÷ 10 000 |
| m² → km² | ÷ 1 000 000 |
(Square the linear factor.)
Volume
| mm³ → cm³ | ÷ 1000 |
| cm³ → m³ | ÷ 1 000 000 |
(Cube the linear factor.)
Time
| seconds → minutes | ÷ 60 |
| minutes → hours | ÷ 60 |
| hours → days | ÷ 24 |
| days → weeks | ÷ 7 |
| days → years | ÷ 365.25 (approx) |
Money
£1 = 100p. Always use consistent units.
Imperial-metric (informal — only basic conversions are tested)
- 1 inch ≈ 2.54 cm.
- 1 foot ≈ 30 cm.
- 1 mile ≈ 1.6 km.
- 1 kg ≈ 2.2 lb.
- 1 litre ≈ 1.75 pints.
✦Worked example
Convert 3.5 hours to minutes and seconds.
- 3.5 × 60 = 210 minutes.
- 3.5 × 3600 = 12 600 seconds.
Worked example: convert 250 ml to litres.
- 250 / 1000 = 0.25 litres.
⚠Common mistakes
- Using time as decimal — 1.5 hours = 90 min, NOT 150 min.
- Forgetting to square/cube for area/volume.
- Mixing capacity and volume symbols — though numerically equivalent (1 ml = 1 cm³).
- Misreading km/h vs km/h or m/s in compound contexts — convert carefully.
- Treating 1 hour as 100 minutes in calculator inputs — must use 60.
➜Try this— Quick check
How many cm² in 0.5 m²?
- 0.5 × 10 000 = 5000 cm².
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