Unit Conversions Cheat Sheet: 25 Conversions You Actually Need

Google this topic and you will get a hundred answers, half of them wrong. Here is the version that holds up. Most unit conversions follow simple multiplication. Memorising 25 of them covers almost every real-world need.

Length

1 inch = 2.54 cm. 1 foot = 30.48 cm. 1 mile = 1.609 km. 1 m = 3.281 ft.

Weight

1 kg = 2.2046 lb. 1 oz = 28.35 g. 1 stone = 6.35 kg. 1 tonne = 1000 kg.

Volume

1 litre = 1.057 US qt = 0.264 US gal. 1 US gal = 3.785 L. 1 cup ≈ 240 ml.

Temperature

°C = (°F − 32) × 5/9. °F = °C × 9/5 + 32. 0°C = 32°F. 100°C = 212°F.

Area

1 acre = 4,047 m² = 43,560 ft². 1 hectare = 10,000 m² = 2.471 acres.

Speed

1 mph = 1.609 km/h. 1 m/s = 3.6 km/h. 1 knot = 1.852 km/h.

Pro tips

• Carry units through every step of a calculation — they catch your mistakes for you.
• Memorise one conversion per category; derive the rest.

Frequently asked questions

Why are US and UK gallons different? Historical drift. 1 US gal = 3.785 L; 1 UK gal = 4.546 L.

Is metric always better? Easier (everything is base-10). Imperial survives in US, UK and a few others by tradition.

Bookmark the calculator linked above — you will need it more often than you think.