Most of the world uses metric. The US still mixes in imperial. Knowing the common conversions saves a lot of head-scratching.
Length
- 1 inch = 2.54 cm
- 1 foot = 30.48 cm
- 1 mile ≈ 1.609 km
- 1 metre ≈ 3.281 feet
Mass
- 1 ounce ≈ 28.35 grams
- 1 pound ≈ 0.454 kg
- 1 kg ≈ 2.205 pounds
Volume
- 1 US gallon ≈ 3.785 litres
- 1 UK gallon ≈ 4.546 litres
- 1 cup ≈ 240 ml (US)