How to Convert Gallons to Liters

To convert gallons to liters, multiply the gallons by 3.78541 for US gallons, so 5 gallons equals 18.93 liters, or by 4.54609 for imperial gallons, so 5 imperial gallons equals 22.73 liters. Always confirm which gallon you mean first, because the two gallons differ by about 20 percent. Convert any volume instantly with our free unit converter.

The Formula: Gallons Times 3.78541 for US Gallons

The formula for US gallons is liters = gallons times 3.78541, and it never changes, because the US gallon is legally defined as exactly 231 cubic inches, which works out to 3.785411784 liters. One US gallon is 3.78541 liters, two gallons is 7.57082 liters, five gallons is 18.92706 liters, and ten gallons is 37.85412 liters, all by the same single multiplication. The reverse formula is gallons = liters divided by 3.78541, so 18.93 liters divided by 3.78541 returns 5 gallons, confirming the round trip. Most people round the factor to 3.785 for everyday use, and that is fine for fuel tanks, aquariums, and paint cans, where the difference is a few milliliters. Keep the full 3.78541 only for lab work, fuel-economy testing, or any calculation where a small error multiplies across thousands of gallons. The most common error is dividing instead of multiplying, which gives a smaller number when the answer must always be larger, because a liter is much smaller than a gallon. If your result is smaller than your starting gallons, you ran the conversion backwards. For a single value without the arithmetic, the free unit converter gives the figure at once, and our liters to gallons converter runs the reverse direction for the same reason.

US Gallon vs Imperial Gallon: The Trap That Changes the Answer

The word gallon names two different volumes, and mixing them up is the single biggest source of wrong answers. The US gallon is 3.78541 liters, while the imperial gallon used in the United Kingdom is 4.54609 liters, about 20 percent larger. The difference comes from history: the US kept the old Queen Anne wine gallon of 231 cubic inches, while Britain redefined its gallon in 1824 as the volume of ten pounds of water. A British recipe, fuel-economy figure, or aquarium guide that says gallons almost always means imperial gallons, while an American source means US gallons. So 10 gallons of petrol in a UK car review is 45.46 liters, but 10 gallons of gas in a US review is 37.85 liters, and treating one as the other throws a fuel-range calculation off by nearly eight liters. The clue is usually the source: UK publications, older Commonwealth texts, and British car magazines use imperial, while US sources use US gallons. When no country is given, check the context for other units: miles per gallon figures above 40 for an ordinary car usually signal imperial gallons, because the same car reports a lower number in US gallons. Our fluid ounces to liters converter has the same US-versus-imperial trap, since the US fluid ounce and the imperial fluid ounce also differ, and the liters to ounces guide explains how to keep the two systems straight.

Gallons to Liters Conversion Chart

A short chart covers most everyday values, and it is worth memorizing the first few rows. One US gallon is 3.79 liters, two gallons is 7.57 liters, three gallons is 11.36 liters, four gallons is 15.14 liters, five gallons is 18.93 liters, and ten gallons is 37.85 liters. For imperial gallons, one is 4.55 liters, two is 9.09 liters, five is 22.73 liters, and ten is 45.46 liters. The pattern is simple enough to extend: every extra US gallon adds 3.78541 liters, and every extra imperial gallon adds 4.54609 liters, so 20 US gallons is 75.71 liters and 20 imperial gallons is 90.92 liters. For values between chart rows, multiply directly rather than guessing between rows, because interpolation errors grow with the gap. A useful mental shortcut is that four US gallons is very close to 15 liters, which is accurate to within one percent, and one imperial gallon is very close to four and a half liters. Painters use the five-gallon row constantly, since paint is sold in five-gallon buckets in the US, and 18.93 liters is the figure that appears on metric labels. Aquarists use the ten-gallon row the same way, since ten-gallon tanks are a standard size, and our 10-gallon fish tank guide works through that exact conversion with stocking and water-change math.

Worked Examples: Fuel, Aquariums, and Paint

Fuel economy is where this conversion earns its keep. A car with a 12-gallon US tank holds 12 times 3.78541, which is 45.42 liters, and if it travels 360 miles on that tank, its economy is 30 miles per gallon, or 360 divided by 45.42, which is 7.93 miles per liter. The same car described in imperial gallons would show a larger tank and a higher miles-per-gallon figure for the identical car, which is why cross-country fuel comparisons must state the gallon. Aquarium math is simpler: a 20-gallon US tank holds 75.71 liters, and a 25 percent weekly water change is 5 gallons, or 18.93 liters, which tells you the size of bucket to buy. Paint coverage works the same way: a paint rated at 400 square feet per gallon covers 400 square feet per 3.78541 liters, so a five-gallon bucket covers about 2,000 square feet, and converting first avoids ordering a second bucket mid-job. A home-brewing example shows the trap clearly: a recipe calling for 5 imperial gallons of wort needs 22.73 liters of fermenter space, but a brewer who uses the US factor plans for only 18.93 liters and ends up nearly four liters short. In every case the method is identical: identify the gallon, multiply by the right factor, and sanity-check the size of the answer against a known row of the chart.

Five Mistakes That Break Gallon Conversions

The first mistake is using the wrong gallon, which we covered above, and it is worth repeating because it causes the largest errors. The second is dividing instead of multiplying, which produces an answer smaller than the starting gallons and should always trigger suspicion. The third is rounding too early: rounding 3.78541 to 3.8 is harmless for one tank, but rounding an intermediate result to a whole number before multiplying again compounds the error, so keep two extra digits until the final step. The fourth is confusing gallons with fluid ounces, since a US gallon contains 128 US fluid ounces, and a reader who converts ounces instead of gallons lands a factor of 128 away from the right answer. The fifth is trusting a search snippet without checking the gallon: many quick answers online never say US or imperial, and the number they show may be the other gallon. The defense against all five is the same three-second check: state the gallon, state the factor, and check that the answer is bigger than the gallons and roughly four times larger. For a single value without the arithmetic, the free unit converter gives the figure at once, and our ounces to cups guide covers the smaller volume step that often appears beside gallon conversions.

Going the Other Way: Liters Back to Gallons

The reverse conversion is liters divided by 3.78541 for US gallons, or liters divided by 4.54609 for imperial gallons. Twenty liters is 5.28 US gallons, fifty liters is 13.21 US gallons, and one hundred liters is 26.42 US gallons. For imperial gallons, twenty liters is 4.40 gallons, fifty liters is 11.00 gallons, and one hundred liters is 22.00 gallons. The reverse direction matters most when reading metric labels: a European car with a 55-liter tank holds 14.53 US gallons, a 200-liter water butt holds 52.83 US gallons, and a 1,000-liter heating-oil delivery is 264.17 US gallons. The same direction check applies: the gallon answer must be smaller than the liter figure, roughly one quarter of it, because a gallon is roughly four liters. A quick estimate is to divide liters by four and then add about five percent for US gallons, since the true divisor is 3.78541 rather than 4. For imperial gallons, divide liters by four and a half, which is close enough for shopping and gardening estimates. When the exact figure matters, use the full factor and the liters to gallons converter rather than the estimate, and keep the US-versus-imperial choice explicit in your notes so the next person reading them converts the same way you did.