A US gallons to liters calculator converts a US-customary volume to the metric liter using 1 US gal = 3.785411784 L (exact). Enter the gallon value and the calculator returns the liter equivalent.
Useful for fueling rental cars in metric countries, sharing recipe quantities across borders, sizing aquariums and pools when the spec is metric-only, and any setting where the same volume needs both unit systems. This calculator uses US gallons specifically, see the UK gallon section below if your source uses imperial measure.
Key takeaway
A US gallon is roughly 3.8 liters. Multiplying by 4 gets you within 6%, which is fine for casual reference. Be aware of the imperial vs. US gallon distinction: imperial gallons are about 20% larger (4.546 L). Most modern uses are US gallons; verify when working with UK historical or marine references.
How it's calculated
The conversion:
liters = US gallons × 3.785411784
The 3.785411784 figure is the US gallon's exact volume in liters, derived from its 231-cubic-inch definition (231 in³ × 16.387064 mL/in³ = 3,785.4 mL = 3.785 L).
For imperial gallons, multiply by 4.54609 instead. The imperial gallon was historically used across the British Empire and is still occasionally referenced in UK marine and aviation contexts, but is deprecated for retail. Source documents predating the UK's metric transition (1965-1995) often need careful unit checking.
Source: NIST exact conversion, 1 US gallon = 3.785411784 L
Examples
1 US gallon, milk jug standard
- Volume 1 gal
1 US gallon converts to 3.785 L, the volume of a standard US milk jug. The metric equivalent in European supermarkets is the 4-liter container, which holds 1.057 US gallons (about 5.7% more). This small gap is why directly substituting milk container sizes between markets gets pricing comparisons slightly off.
15 US gallons, typical sedan tank
- Volume 15 gal
15 US gallons is 56.78 L, typical for a midsize sedan tank. A European tank of the same physical capacity would be quoted as "57-liter tank" on the spec sheet. At $3.50/gal that's $52.50 to fill; the same liters at €1.50/L cost €85, illustrating how fuel pricing dominates cross-system tank-size comparisons.
Frequently asked questions
How do I convert US gallons to liters?
Multiply by 3.785 for the precise answer, or by 4 for a quick estimate within ~6%. So 12 gal × 3.785 = 45.4 L (or 12 × 4 = 48 L, close but a few liters high). For high-precision contexts (chemistry, engineering), use the full 3.785411784 factor.
How big is a US gallon vs. an imperial gallon?
US gallon = 3.785 L (defined as 231 cubic inches). Imperial gallon = 4.546 L, about 20% larger, defined in the UK as the volume of 10 lb of water at a specific temperature. Modern UK retail uses liters; imperial gallons mostly appear in older/legacy contexts. Always verify which "gallon" your source means before converting.
How many liters in a barrel?
Depends on the barrel. A US oil barrel = 42 US gal = 158.987 L (the global standard for crude oil pricing). A US fluid barrel = 31.5 gal = 119.24 L (used for some beverages historically). A UK beer barrel = 36 imperial gal = 163.66 L. The 42-gallon oil barrel is the most-quoted figure globally, that's what "$80 a barrel" pricing references.
How do I convert a recipe from US to metric?
For volumes, multiply gallons by 3.785, quarts by 0.946, cups by 0.237 to get liters. For weights (which are different and matter more in baking), multiply ounces by 28.35 or pounds by 453.6 to get grams. Many serious cooks recommend going by weight in metric rather than volume in either system, weights are unambiguous and don't depend on packing density (a cup of flour can vary 20% by weight depending on how you scoop it).