Gallon to Liter Calculator
Convert gallons to liters instantly — with a US vs UK (imperial) gallon toggle, since the two are different sizes and mixing them up is the single most common mistake in this conversion.
Convert Any Value
Choose which gallon you mean, then enter a value in either unit.
3.7854 L
Gallons and Liters at a Glance
The liter is the standard volume unit in the metric system, used worldwide for fuel, beverages, and liquid measurement. The gallon is a US customary and imperial unit — but critically, it isn't the same size in both systems, which makes "gallon to liter" one of the few conversions where you have to know which gallon you're starting from before you can get the right answer.
A US liquid gallon equals approximately 3.78541 liters. A UK (imperial) gallon, still used in the UK and some Commonwealth countries for certain contexts, equals approximately 4.54609 liters — about 20% larger than the US gallon. Getting this distinction right matters most for fuel economy figures, recipe scaling, and industrial volume specifications.
The Gallon to Liter Formula
Once you know which gallon type applies, the conversion is a straightforward multiplication.
US Gallon → Liters
Liters = US Gallons × 3.78541
Multiply the number of US gallons by 3.78541 to get liters.
Example: 12 US gal × 3.78541 = 45.42 L
UK Gallon → Liters
Liters = UK Gallons × 4.54609
Multiply the number of UK (imperial) gallons by 4.54609 to get liters.
Example: 12 UK gal × 4.54609 = 54.55 L
Liters → US Gallons
US Gallons = Liters ÷ 3.78541
Example: 50 L ÷ 3.78541 = 13.21 US gal
Liters → UK Gallons
UK Gallons = Liters ÷ 4.54609
Example: 50 L ÷ 4.54609 = 11.00 UK gal
Gallon to Liter Conversion Table
A side-by-side reference showing both gallon types, so it's clear how much they diverge at larger volumes.
| Gallons | Liters (US) | Liters (UK) |
|---|---|---|
| 1 gal | 3.7854 L | 4.5461 L |
| 5 gal | 18.9271 L | 22.7305 L |
| 10 gal | 37.8541 L | 45.4609 L |
| 15 gal | 56.7812 L | 68.1914 L |
| 20 gal | 75.7082 L | 90.9218 L |
| 50 gal | 189.2706 L | 227.3045 L |
| 100 gal | 378.5412 L | 454.6090 L |
For a value not listed here, the calculator at the top of this page computes the exact figure instantly for whichever gallon type you select.
Worked Examples: Step by Step
Example 1: Convert 8 US gallons to liters
- Formula: L = US gal × 3.78541
- 8 × 3.78541 = 30.28
- Answer: 8 US gal = 30.28 L
Example 2: Convert 25 liters to US gallons
- Formula: US gal = L ÷ 3.78541
- 25 ÷ 3.78541 = 6.60
- Answer: 25 L = 6.60 US gal
Example 3: A UK fuel tank holds 12 imperial gallons — how many liters?
- Formula: L = UK gal × 4.54609
- 12 × 4.54609 = 54.55
- Answer: 12 UK gal = 54.55 L
US Gallon vs. UK Gallon: Why It Matters
Because the two gallons differ by roughly 20%, using the wrong one can lead to meaningfully wrong answers — especially at larger volumes like fuel tanks or industrial containers.
| Measure | US Liquid Gallon | UK (Imperial) Gallon |
|---|---|---|
| Liters | 3.78541 L | 4.54609 L |
| Fluid ounces | 128 US fl oz | 160 imperial fl oz |
| Where it's used | United States, Liberia, Myanmar | UK (fuel economy figures), Canada (historically), some Caribbean nations |
| Common context | US fuel prices, US recipes, US paint/container sizing | UK fuel economy (mpg), older British recipes and containers |
A practical rule of thumb: if a figure comes from a US source (gas station, US recipe, US product spec), assume the US gallon. If it comes from a UK source — particularly UK fuel economy figures, which are still often quoted in miles per (imperial) gallon — assume the UK gallon. When the source isn't clear, it's worth double-checking, since the 20% gap is large enough to matter.
Where This Conversion Comes Up
Fuel Economy and Vehicle Specs
US fuel economy is measured in miles per US gallon, while UK fuel economy is measured in miles per imperial gallon — the same "mpg" label describes different things, so comparing a US and UK car's efficiency requires converting through liters first.
Cooking and Recipe Scaling
Older British recipes sometimes use imperial gallons or their subdivisions (imperial pints, quarts) while US recipes use US measures — a distinction that matters when scaling a recipe from one tradition to a metric or different-gallon kitchen.
Fuel Tanks, Water Tanks, and Industrial Containers
Product specifications for tanks, drums, and containers sold internationally often need converting between gallon-based US specs and liter-based specs used elsewhere.
Swimming Pools and Water Usage
US water usage and pool volume figures are often quoted in gallons, while international comparisons and environmental reporting use liters or cubic meters.
Paint, Fuel, and Chemical Purchasing
Paint cans, fuel drums, and chemical containers are sold in gallon sizes in the US and liter sizes elsewhere, so buyers comparing prices per unit volume across regions need to convert first.
Common Mistakes When Converting
- Using the wrong gallon type. The single biggest source of error — a US gallon and a UK gallon differ by about 20%, so picking the wrong one for the source country gives a meaningfully wrong result.
- Assuming "gallon" always means the same thing globally. Only the US (and a few other countries) use the US gallon; most of the rest of the world that still references gallons at all uses the imperial definition.
- Confusing gallons with liters at the pump when traveling. Fuel is sold by the liter in most countries outside the US, so travelers used to gallon-based pricing need to convert to sanity-check what they're paying per unit volume.
- Mixing up dry and liquid gallons. The US also has a separate, less commonly used "dry gallon" (about 4.405 L) for measuring dry goods — nearly all everyday references to "gallon" mean the liquid gallon covered on this page.
Cheat Sheet: Common Round Numbers
| Unit | Value |
|---|---|
| 1 US gal | 3.7854 L |
| 1 UK gal | 4.5461 L |
| 1 L | 0.2642 US gal / 0.2200 UK gal |
| 1 US quart | 0.9464 L |
| 1 US fl oz | 29.5735 mL |
Frequently Asked Questions
How many liters are in a gallon?
A US gallon equals approximately 3.78541 liters. A UK (imperial) gallon equals approximately 4.54609 liters — about 20% more than the US gallon.
Why are there two different gallon sizes?
The US gallon comes from an old English wine gallon measure, while the UK imperial gallon was redefined in 1824 based on the volume of 10 pounds of water — the two standards were never unified.
How do I know which gallon to use?
If the figure comes from a US source, use the US gallon (3.78541 L). If it comes from the UK or a country still using imperial measures, use the UK gallon (4.54609 L).
Is the gallon to liter conversion exact or approximate?
The US gallon is defined as exactly 231 cubic inches, and the UK gallon as exactly 4.54609 liters — both convert to a fixed, non-repeating decimal in liters (3.785411784 L for the US gallon), so the figures used here are precise to five decimal places, which is exact enough for virtually all everyday and professional purposes.
How many liters is a 15-gallon fuel tank?
A 15 US-gallon tank holds about 56.78 liters. A 15 UK-gallon tank holds about 68.19 liters.
Does UK fuel economy (mpg) use the same gallon as the US?
No. UK fuel economy figures use the imperial gallon, which is larger than the US gallon, so a UK car's "mpg" figure isn't directly comparable to a US car's "mpg" figure without converting both through liters first.
Does this calculator handle both gallon types?
Yes. Use the toggle at the top of the calculator to switch between US Gallon and UK (Imperial) Gallon before entering your value.