Convert US gallons to liters instantly — 1 gal is exactly 3.785411784 L, with steps shown.
American gas pumps, aquariums, and water heaters are sized in gallons; the rest of the world buys fuel and tanks in liters. Our free Gallons to Liters Converter multiplies by the exact 3.785411784 factor and shows the step, so fuel economy, tank volumes, and recipe batches convert cleanly.
The US liquid gallon is defined as exactly 231 cubic inches — and since the inch is exactly 25.4 mm, the gallon is exactly 3.785411784 liters. Like the inch itself, the modern gallon is a defined volume, so the conversion factor is exact mathematics.
Enter US gallons and get liters to four decimals, with milliliters and the water-weight equivalent. Drivers, aquarists, and brewers get one transparent multiplication.
Three gallons exist, and mixing them up is the classic error: the US liquid gallon (3.785411784 L), the US dry gallon (4.404884 L, for grain), and the imperial gallon (4.54609 L, UK). This converter uses the US liquid gallon — the one on gas pumps and milk jugs. An imperial gallon is a full 20% larger, so always check which gallon a British or Canadian source means.
The US gallon’s definition — exactly 231 cubic inches — dates to an 18th-century British wine gallon that the US kept while Britain later redefined its own. Because the inch is now exactly 25.4 mm, the gallon computes to exactly 3.785411784 L: 231 × 25.4³ mm³ ÷ 1,000,000.
The liter (1 cubic decimeter) is the metric everyday volume — a liter of water weighs a kilogram, which is why the widget shows the water weight. Fuel, drinks, aquariums, and engine displacements all speak liters outside the US.
Key terms:
The 3.785411784 factor is exact for the US liquid gallon. If your source is British or pre-metric Canadian, you likely need the imperial 4.54609 factor instead.
A car takes 14.2 gallons at the pump. How many liters is that?
European drivers would call it a “54-liter fill” — the converter gives the exact figure for expense logs.
A 55-gallon aquarium: what is its metric volume, and how much does the water weigh?
The weight figure is the point: a “55-gallon” tank needs a stand rated for nearly half a ton with substrate and glass.
Hannah drives 2,400 miles on a road trip and burns 78 gallons. Her European friend asks for the fuel in liters: 78 × 3.785411784 = 295.26 L. The friend then computes 7.4 L/100 km from the 3,862 km distance — the converter’s exact liter figure keeps the efficiency math honest.
A second scenario: a home brewer scales a 5-gallon batch to metric carboys: 5 × 3.785411784 = 18.927 L — a standard 19 L corny keg fits perfectly. The converter just prevented a batch sized for a vessel that doesn’t exist.
A third: a pool owner’s 20,000-gallon pool needs metric chemical dosing: 20,000 × 3.785411784 = 75,708 L. The chlorine chart wants grams per 10,000 L, so the exact volume is the foundation of safe dosing.
A fourth: a classic-car importer reads a UK road test quoting 30 mpg imperial. Converting the gallons first — imperial gallons are 4.54609 L — before comparing to US mpg figures. The converter handles US gallons; the imperial warning in the formula box handles the rest.
Fuel: the US prices by the gallon; nearly everywhere else by the liter. The $3.50/gallon sign is $0.9246/L — and cross-country price comparisons must convert before they can outrage or reassure.
Aquariums: tank sizes are nominal gallons in the US (a “55-gallon” is 208 L) and liters elsewhere. Stand ratings, heater wattage, and filter flow all scale with the true volume.
Brewing: American homebrew is 5-gallon batches (18.9 L); the metric world brews 20 L. Equipment — kettles, fermenters, kegs — is sized to these standards, so conversion decides what fits.
Water heaters: US tanks are 40/50 gallons (151/189 L); European combi boilers are rated in L/min. Replacing one system with the other starts with volume conversion.
Paint: sold by the gallon in the US (3.785 L) and the liter elsewhere. Coverage math — m² per coat — needs the true volume before the second coat is bought.
Agriculture: spray rates in gallons per acre meet metric chemical labels in liters per hectare. The double conversion (volume and area) is where applicators earn their certification.
Engines: displacement in liters globally, with cubic inches lingering in American V8 culture (350 ci = 5.7 L). Fuel tanks follow the same split: gallons vs. liters.
One pattern worth internalizing: always ask which gallon. US liquid is the default in this converter; imperial is 20% larger; dry is for grain. The unit’s name is the same — the volume isn’t.Home heating: oil is delivered in gallons in the US Northeast; burners are rated in liters per hour elsewhere. A 275-gallon tank holds 1,040.99 L — the delivery ticket both driver and homeowner sign.
Winemaking: barrels are 59 gallons (225 L) for Bordeaux barriques; the metric world thinks 225. A 59-gal barrel is 223.34 L — close, but the converter settles it.
Car detailing: product dilutions are ounces per gallon in the US, milliliters per liter elsewhere. A 5-gallon wash bucket is 18.93 L — the ratio math starts here.
Firefighting: tanker capacities are gallons in the US (a 2,000-gallon tender = 7,570.82 L). Mutual-aid across the Canadian border converts every dispatch.
Distilling: still charges are gallons in American craft distilling, liters in Scotland. A 500-gallon wash is 1,892.71 L — the mash bill’s first number.
231 cubic inches of history: the US gallon is 231 cubic inches because Queen Anne’s 1707 wine gallon was — a standard the young United States kept while Britain later redefined its own gallon to 277.42 cubic inches (the imperial gallon, 4.54609 L). So America’s gallon is a frozen 18th-century British wine measure, and its exact liter value (3.785411784) falls out of the exact inch: 231 × 25.4³ mm³ = 3,785,411.784 mm³. The converter multiplies by this exact figure — not a measured quantity but a computed consequence of two definitions. Every gas pump in America is, legally speaking, dispensing 18th-century wine gallons by the cubic inch.
Worked scenario — the fuel-economy comparison: a reviewer compares a US car at 32 mpg with a European car at 6.0 L/100 km. Convert the American figure: 32 miles = 51.499 km; 1 gallon = 3.78541 L; so 3.78541 L per 51.499 km = 7.35 L/100 km. The European car wins by 1.35 L/100 km — but the reviewer’s real work was checking the gallons: the UK press kit quoted 38 mpg imperial, which is 38 × 4.54609 = 172.75 L per 61.16 km … no wait — per 38 miles = 61.16 km, giving 7.43 L/100 km only if you mistakenly use US gallons; correctly, 38 imperial mpg = 7.43 × (4.54609/3.78541) = 8.93 L/100 km. The gallon’s identity is the whole story — the converter handles US gallons exactly, and the formula box warns about the imperial impostor.
Edge cases and pro tips: always identify the gallon first: US liquid (3.78541 L) for fuel and liquids, imperial (4.54609 L) for UK legacy figures, dry (4.40488 L) for grain — the same word, three volumes, 20% spread. When converting fuel economy, use the dedicated identities (235.214 ÷ mpg-US = L/100 km) rather than chaining volume and distance conversions by hand; fewer steps, fewer slips. For aquariums, the nominal gallons are approximate — measure the tank’s actual dimensions and compute liters geometrically for stocking decisions, using the converter only for the nominal-to-metric translation. And the water-weight bonus (1 L = 1 kg) is exact for practical purposes — a 200 L water change is 200 kg, the number that decides whether the floor joists care.
Gallons to liters (US liquid): L = gal x 3.785411784 (exact; 231 in³). Imperial gallon = 4.54609 L (20% larger). 1 L water = 1 kg. Source: Sigma Calculator, Gallons to Liters Converter, https://sigmacalculator.net/math-calculators/gallons-to-liters-converter/
Cite this page as: Gallons to Liters Converter, Sigma Calculator, https://sigmacalculator.net/math-calculators/gallons-to-liters-converter/
Last updated: October 12, 2026