Metric and Imperial Conversions
Kilometres or miles, kilograms or pounds, Celsius or Fahrenheit. Understand how metric works, then learn the handful of conversions worth memorising.
~8 min4 lessonsInteractive converter5-question quiz
01
How the metric system works
Metric units go up in steps of 10, and the prefix tells you the step:
| Prefix | Means | Example |
|---|---|---|
| kilo- (k) | × 1,000 | 1 kilometre = 1,000 metres |
| centi- (c) | ÷ 100 | 1 metre = 100 centimetres |
| milli- (m) | ÷ 1,000 | 1 litre = 1,000 millilitres |
So converting within metric is just moving the decimal point: 2.5 km = 2,500 m; 750 ml = 0.75 l.
Neat link: 1 litre of water weighs 1 kilogram, and fills a 10 cm × 10 cm × 10 cm cube.
02
Length and weight
| From | To | Multiply by | Quick estimate |
|---|---|---|---|
| inches | centimetres | 2.54 (exact) | × 2.5 |
| feet | metres | 0.3048 | ÷ 3.3 |
| miles | kilometres | 1.609 | × 1.6 (or × 8 ÷ 5) |
| kilometres | miles | 0.621 | × 0.6 |
| pounds | kilograms | 0.4536 | ÷ 2.2, or halve and take off 10% |
| kilograms | pounds | 2.205 | × 2.2 |
Example · 10 km run in miles
- 10 × 0.621
- ≈ 6.2 miles
03
Volume and cooking
| Unit | Metric equivalent |
|---|---|
| 1 teaspoon (tsp) | ≈ 5 ml |
| 1 tablespoon (tbsp) | ≈ 15 ml (3 tsp) |
| 1 US cup | ≈ 240 ml |
| 1 US fluid ounce | ≈ 29.6 ml |
| 1 US gallon | ≈ 3.79 litres |
| 1 UK (imperial) gallon | ≈ 4.55 litres |
US and UK differ. A UK pint is 568 ml; a US pint is 473 ml. Recipes from the other side of the Atlantic can be off by 20%.
For baking, weighing in grams is more accurate than cups: a cup of flour can vary by 30 g depending on how it's packed.
04
Temperature
°F = °C × 9/5 + 32 · °C = (°F − 32) × 5/9
Quick estimate: °C to °F, double it and add 30. °F to °C, subtract 30 and halve. Close enough for weather.
| °C | °F | Feels like |
|---|---|---|
| 0 | 32 | Water freezes |
| 10 | 50 | Jacket weather |
| 20 | 68 | Room temperature |
| 30 | 86 | Hot day |
| 37 | 98.6 | Body temperature |
| 100 | 212 | Water boils |
| 180 | 356 | Moderate oven |
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