How Many Liters in a Gallon? US vs Imperial

June 29, 2025 • 4 min read

The gallon is used for everything from fuel to milk to paint — but not all gallons are equal. The US gallon and the Imperial (UK) gallon are different sizes, which causes confusion when comparing prices, fuel economy, or recipes across countries.

The Answer

Why Two Different Gallons?

Both come from English measurement history but diverged in the early 1800s:

• ▶ The US adopted the Queen Anne wine gallon (231 cubic inches) when it became independent
• ▶ Britain redefined the gallon in 1824 as the volume of 10 pounds of water (277.4 cubic inches)
• ▶ Result: the Imperial gallon is larger because it was based on weight of water rather than an arbitrary volume

Gallon Breakdown

• ▶ 1 US gallon = 4 US quarts = 8 US pints = 128 US fl oz = 3,785 mL
• ▶ 1 Imperial gallon = 4 Imperial quarts = 8 Imperial pints = 160 UK fl oz = 4,546 mL
• ▶ 1 US gallon = 0.833 Imperial gallons
• ▶ 1 Imperial gallon = 1.2 US gallons

Practical Examples

• ▶ Fuel: Gas at $3.50/US gallon = $0.92/liter. Petrol at £1.50/liter = £6.82/Imperial gallon = about $5.68/US gallon
• ▶ Swimming pool: A typical pool holds 15,000 US gallons = 56,781 liters
• ▶ Daily water intake: The recommended "8 glasses" is about half a US gallon = 1.9 liters
• ▶ Paint coverage: 1 US gallon of paint covers about 350-400 sq ft

Who Uses Which?

• ▶ US gallon: United States, some Latin American countries (for fuel)
• ▶ Imperial gallon: Was used in UK, Canada, Australia — now mostly replaced by liters
• ▶ Liters: The rest of the world (official metric unit)

Even the UK and Canada have largely abandoned the gallon. Fuel is sold by the liter in both countries now, though Canadians still occasionally reference gallons colloquially.

Quick Mental Math

For US gallons to liters, multiply by 4 and subtract a little (technically multiply by 3.785). For a quick estimate, think "just under 4 liters per gallon." A 20-gallon fuel tank holds about 76 liters.