⚖️ Comparison · Updated for 2026
UK Gallon vs US Gallon
Side-by-side comparison, when-to-use-each guide, and instant conversion. Reviewed for 2026.
Quick answer: 1 UK gallon = 4.546 litres. 1 US gallon = 3.785 litres. The UK gallon is 20% bigger. Old UK MPG figures are about 20% better than US MPG for the same engine, purely because the gallon is bigger — not because British cars were more efficient.
Decision guide — when to use which
Use UK Gallon when…
UK fuel economy (MPG), some commodity trading, Caribbean nations using UK system.
Use US Gallon when…
US fuel pumps (universal), US fuel economy, fuel pricing in Latin America linked to US standards.
📊 Side-by-side comparison
| Aspect | UK Gallon | US Gallon |
|---|---|---|
| Volume | 4.546 L | 3.785 L |
| Quarts | 4 | 4 |
| Pints | 8 UK pints (568 ml each) | 8 US pints (473 ml each) |
| Fuel economy comparison | UK MPG figure × 0.83 ≈ US MPG | US MPG × 1.2 ≈ UK MPG |
Frequently asked
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My old car says 40 MPG (UK). What's that in US MPG?
40 MPG UK × 0.83 = 33.3 MPG US. The factor is exact: 0.8327. The reason for the difference is purely the bigger UK gallon, not driving habits.
?
Why do US and UK gallons differ?
After American independence in 1776, the US continued using the older 'wine gallon' (3.785 L) while the UK standardised on a larger 'Imperial gallon' (4.546 L) in 1824. Both are descendants of pre-1776 British units.
Reviewed for 2026. All conversion factors and historical references verified against official sources (ISO standards, government weights & measures legislation, IEC technical specifications). Built by a UK-based qualified primary teacher and FA Level 2 coach as part of 247QuickTools' free utility-tools project. We don't sell SEO links or accept paid placements in this content.