Worked example 1
Convert 25 °C to °F.
- 25 × 9 = 225.
- 225 ÷ 5 = 45.
- 45 + 32 = 77.
Answer: 77 °F
Reference Sheets · Reference
Metric and imperial conversions reference
The metric system (grams, metres, litres) is used in science and most countries. Imperial units (inches, pounds, pints) are still common in the UK and USA.
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Before you start
Who it's for and what to know first
Multiplying and dividing by 10, 100 and 1,000.
Learn it
How it works
- Metric length: 10 mm = 1 cm; 100 cm = 1 m; 1,000 m = 1 km.
- Metric mass: 1,000 g = 1 kg. Volume: 1,000 ml = 1 litre.
- Approximate imperial: 1 inch ≈ 2.54 cm; 1 foot = 12 inches ≈ 30 cm; 1 mile ≈ 1.6 km; 1 kg ≈ 2.2 lb; 1 UK pint ≈ 568 ml (a US pint is smaller, about 473 ml).
- Temperature: °F = °C × 9 ÷ 5 + 32. Water freezes at 0 °C (32 °F) and boils at 100 °C (212 °F).
- Bigger unit to smaller → multiply. Smaller unit to bigger → divide.
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Practice questions
Tips
Common mistakes
- Multiplying when you should divide — ask: will the number get bigger or smaller?
- Multiplying when you should divide. Converting to a bigger unit gives a smaller number.
Last reviewed: 25 September 2026