Metric vs Imperial Units: A Conversion Guide
Most of the world uses the metric system; a few countries (notably the US) still use imperial units for everyday measurements. Knowing the key conversion factors — and where they trip people up — saves mistakes in cooking, travel, DIY and science. The unit converter covers every category below at once.
Length and distance
- 1 inch = 2.54 cm exactly; 1 foot = 30.48 cm.
- 1 metre ≈ 3.281 feet.
- 1 mile ≈ 1.609 km (so a 5K ≈ 3.11 miles).
Convert any of these instantly with the length converter.
Weight and mass
- 1 kilogram ≈ 2.205 pounds.
- 1 pound = 16 ounces ≈ 453.6 grams.
- 1 stone = 14 pounds ≈ 6.35 kg (common for body weight in the UK).
The weight converter handles kg, lb, oz and stone together.
Temperature
Temperature is the one that catches people out, because the scales do not share a zero point. °F = °C × 9/5 + 32, and °C = (°F − 32) × 5/9. So 20°C = 68°F, and 100°C (boiling) = 212°F. The temperature converter does it both ways, plus Kelvin.
Volume — watch the gallon
A common pitfall: the US and imperial (UK) gallons are different. A US gallon ≈ 3.785 litres, while an imperial gallon ≈ 4.546 litres — about 20% larger. US cups, pints and fluid ounces differ from UK ones too, which matters in recipes.
Common pitfalls
- Mixing US and imperial volumes — always check which gallon or cup a recipe means.
- Forgetting temperature has an offset (you can't just scale °C to °F).
- Confusing weight ounces with fluid ounces — they measure different things.
When in doubt, let the converter do the arithmetic so a misplaced factor doesn't ruin a measurement.