Gallon to Litre: US vs UK, Conversion & Calculator

If you’ve ever tried to fill a car with fuel in the UK after reading US road-trip guides, you know the confusion: one gallon in America doesn’t match one gallon in Britain. The gallon is one of those units that sounds simple but trips up travellers, cooks and engineers alike.

US gallons in 1 liter: 0.264172 ·
Liters in 1 US gallon: 3.785411784 ·
Liters in 1 UK gallon: 4.54609 ·
Liters in 1 US dry gallon: 4.40488377086 ·
Ratio US gallon : UK gallon: 0.832674

Seven key conversions sum up the difference between the three gallon types and their litre equivalents.

How many litres are in a gallon?

The answer is never a single number. Three different gallon definitions exist, each with its own litre equivalent.

US liquid gallon vs UK imperial gallon

The US liquid gallon – used for most everyday liquids in the United States – is defined as exactly 231 cubic inches, which equals 3.785411784 litres, according to the NIST Office of Weights and Measures (US official measurement authority). The UK imperial gallon, used in the United Kingdom, Ireland (historically), and some Commonwealth countries, is larger: 1 imperial gallon equals exactly 4.54609 litres, per UK Government guidance on weights and measures. The imperial gallon is about 20% bigger than its US counterpart.

US dry gallon definition

Less commonly encountered, the US dry gallon is used for dry commodities such as grains and produce. It measures 4.40488377086 litres, making it larger than the US liquid gallon but smaller than the UK imperial gallon (Encyclopaedia Britannica – same source as timeline). Most everyday conversions ignore the dry gallon, but it matters for agricultural trade.

Conversion formula

• US gallons to litres: multiply by 3.785411784 (UnitConverters.net – US gallon converter)
• UK gallons to litres: multiply by 4.54609 (UnitConverters.net – UK gallon converter)
• US dry gallons to litres: multiply by 4.40488377086

The implication: when someone says “a gallon of petrol” or “a gallon of water,” the actual volume changes by up to 20% depending on which side of the Atlantic you are on.

Is 4 liters equal to 1 gallon?

A common rule of thumb says “a litre is roughly a quart” and “4 litres make a gallon.” But the math tells a different story.

4 litres to US gallons

Four litres convert to 1.056688 US gallons (UnitConverters.net – US gallon converter). That is just over one US gallon – a difference of about 5.7%.

4 litres to UK gallons

Four litres equal 0.879877 UK gallons (UnitConverters.net – UK gallon converter). In UK terms, 4 litres is well short of a full gallon.

Three gallon types, one clear pattern: none of them equals exactly 4 litres.

The catch: the 4‑litre ‘gallon’ shorthand works reasonably for US liquid gallons but badly for UK gallons. In recipes or fuel calculations, relying on the approximation can lead to measurable over- or under-measurement.

How many litres of fuel are in a gallon in the UK?

At UK petrol pumps, fuel is sold by the litre, but fuel economy figures – miles per gallon (MPG) – still use the imperial gallon.

UK petrol gallon conversion

One imperial gallon of petrol equals 4.54609 litres (UK Government guidance – same source as earlier). When you see a car advertised at 50 MPG (UK), that means it can travel 50 miles on 4.54609 litres of fuel.

• 1 gallon (UK) petrol = 4.54609 litres
• 10 gallons (UK) petrol = 45.4609 litres
• 20 gallons (UK) petrol = 90.9218 litres

Practical example: cost per litre vs per gallon

Suppose petrol costs £1.50 per litre. A UK gallon costs £1.50 × 4.54609 = £6.82. In contrast, a US gallon at the same per‑litre price would cost £1.50 × 3.7854 = £5.68 – a difference of over £1 per gallon. Which? (UK consumer advocacy group) notes that comparing fuel prices across countries without adjusting for the gallon type leads to significant errors.

For Ireland, Citizens Information – same source as earlier – states that fuel is sold in litres and road signage is metric, but older imperial references still appear in casual conversation.

Why this matters: if you are comparing a UK car’s MPG with a US car’s MPG, the gallon unit itself skews the numbers by about 20%.

Why are American gallons different from UK gallons?

The two gallon standards diverged nearly 200 years ago, and they have stayed separate ever since.

History of the US customary system

The US gallon traces its origin to the Queen Anne wine gallon of 1707, which measured exactly 231 cubic inches. When the US became independent, it kept this definition as part of the US customary system. NIST continues to use that same standard today: 1 US gallon = 231 in³ = 3.785411784 L.

Imperial system origins

In 1824, the British Parliament decided to standardise on a single unit — the imperial gallon — based on the volume occupied by 10 pounds of distilled water. That volume turned out to be about 277.42 cubic inches, or 4.54609 litres. Encyclopaedia Britannica notes that the US did not adopt the change, so two entirely separate gallon definitions have coexisted ever since.

“The gallon is not a single universal unit; the meaning depends on whether the US customary or imperial system is being used.”

— UnitConverters.net (online conversion tool – same source as US gallon converter)

The trade-off: historical accident created a measurement gap that still confuses consumers, travellers, and industries today.

How to convert gallons to litres accurately?

Getting it right every time requires knowing which gallon you have and using the correct conversion factor.

Manual formula

1. Identify your gallon type: US liquid, UK imperial, or US dry.
2. Multiply by the exact factor:
   – US liquid × 3.785411784
   – UK imperial × 4.54609
   – US dry × 4.40488377086
3. Check your result with an online calculator or cross‑reference table.

Calculator tools

• UnitConverters.net – reliable but default to US unless told otherwise.
• Excel’s =CONVERT function: use “gal” for US and “uk_gal” for UK (YouTube tutorial – same source as earlier).
• Many online calculators default to US gallons – always check the dropdown (OVACEN – same source as earlier).

Quick reference table: 1 to 10 gallons to litres

Use the table below for common volumes – double‑check the column label to avoid mixing systems.

The pattern: the difference between US and UK values grows linearly with volume. At 10 gallons, the gap is over 7.6 litres – more than a whole extra gallon in US terms.

“The imperial gallon is also called the UK gallon in many consumer calculators and conversion tables.”

— MPG Calculator (UK motoring site)

For weight conversions that use a similar imperial‑to‑metric logic, see our guide 135 Pounds in KG: Converter, Charts & Health Guide. And for more on water volumes and availability, check Distilled Water Woolworths: David Gray’s 2L/4L Availability.

For those needing precise figures, a detailed guide on exact US and UK conversions breaks down the exact US and UK gallon-to-litre values.

Frequently asked questions

“1 liter equals approximately 0.264172 US gallons and 0.219969 imperial gallons.”

— UnitConverters.net (conversion tables – same source as US gallon converter)

For a traveller buying fuel in the UK with US expectations, the difference means paying about 20% more per gallon than you think – so always convert using the right factor. The same applies to recipes, water intake goals, and any measurement that crosses the Atlantic.