US Gallon vs UK Gallon: The Key Difference
The US customary gallon was derived from the old English wine gallon; the UK imperial gallon from the older ale gallon. They diverged permanently in 1824 when Britain standardised the imperial system.
- 1 US gallon = 3.785411784 liters (exact by definition)
- 1 UK (imperial) gallon = 4.54609 liters (exact by definition)
- UK gallon is ~20.1% larger than the US gallon
- Canadian fuel efficiency is also quoted in L/100km (not gallons) — a European-style metric
Real-World Reference Volumes
Common volumes you'll encounter when dealing with fuel, beverages, or engine specifications:
- Small car fuel tank: 40–50 L (10.6–13.2 US gal)
- Mid-size car fuel tank: 55–65 L (14.5–17.2 US gal)
- SUV / truck fuel tank: 70–100 L (18.5–26.4 US gal)
- Keg of beer (US half-barrel): 58.67 L = 15.5 US gal
- US beer keg (quarter-barrel / pony keg): 29.34 L = 7.75 US gal
- Swimming pool (average backyard): ~75,000 L = ~19,800 US gal
MPG Conversion: US ↔ UK ↔ L/100km
Fuel economy is quoted differently by market: US uses MPG (US), UK uses MPG (UK), and most of the world uses L/100km (lower is better). Converting between them is essential when comparing international car reviews.
- MPG (US) to L/100km: divide 235.215 by MPG (US)
- L/100km to MPG (US): divide 235.215 by L/100km
- MPG (UK) to MPG (US): multiply by 0.8327
- MPG (US) to MPG (UK): multiply by 1.2009
- Example: 50 MPG (UK) = 41.6 MPG (US) = 5.65 L/100km