1 liter is 0.2641720524 US gallons

Liters into gallons is a division, and the divisor is exact. NIST Handbook 44 Appendix C defines one US liquid gallon as 3.785411784 liters, so:

1 L = 1 / 3.785411784 = 0.2641720524 US gallons

Flip it and you get the more familiar reminder that a gallon is a little under 3.8 liters, so a liter is a little over a quarter of a gallon. That quarter picture is the fastest mental estimate: double the liters, halve the gallons, and you land within a few percent of the exact figure.

The NIST Special Publication 811 table lists the same gallon factor, and the liter is the SI derived unit for volume, so the liter side of every conversion here is exact by definition.

NIST Special Publication 811, Appendix B.8 and Handbook 44 Appendix C (PDF) are the two tables to check if you ever need to defend the factor to a pedantic coworker.

Soda, water and juice bottles in gallons

Most drink containers are sized in liters or milliliters, and the US label often adds fluid ounces. One liter is 33.8140227 US fluid ounces and 4.2267528 cups, so a 2 liter soda bottle is 0.5283441047 gallons, 67.6280454 fluid ounces and 8.4535057 cups. Four 2 liter bottles are 2.1133764 gallons, so they cover a one gallon recipe and leave 0.1133764 gallons, about 14.5 fluid ounces, over.

Store cases convert the same way. A 24 pack of 500 mL bottles totals 12 liters, which is 3.1700646 gallons. A single 500 mL bottle is 16.9070113 fluid ounces, so the "16.9 fl oz" printed on the label is just 500 mL rounded to one decimal. A 1.5 liter bottle is 0.3962580785 gallons, the size most store brand juice comes in.

Gasoline: liters at the pump versus gallons at the pump

Fuel is the place where the liter gallon gap costs real money. Canadian and European pumps sell by the liter, US pumps by the gallon, and the bridge rate is one US gallon = 3.785411784 L. A liter priced at $1.00 works out to $3.785411784 per gallon; a liter at $1.50 is $5.678117676 per gallon. Reading the other direction, $3.50 per gallon is $0.9246022 per liter, which is how a cross border driver checks whether the Canadian pump price beats the US one.

Tank sizes mix units too. A compact car with a 60 liter tank carries 15.8503231 US gallons; at 30 miles per gallon that tank drives 475.5 miles, and 30 mpg is 7.84 liters per 100 km in the metric figure a European brochure would print. The Energy Information Administration's gasoline explained page tracks US prices per gallon, so any liter quote from abroad has to be multiplied by the price factor above before it compares.

To read the table backwards, take a US pump price and divide by 3.785411784: a 5.00 dollar per gallon pump price is 1.32 dollars per liter to the nearest cent.

Milk, wine and recipe measures

Recipes sit on top of cups, and cups convert exactly: one US cup is 236.5882365 mL, so a liter of milk is 4.2267528 cups. A recipe asking for 4 cups wants 0.946352946 liters, which is one US quart to within rounding, since 1 liter is 1.0566882 quarts. Buy the liter carton and you have about 3 percent more than the quart the recipe names.

Wine bottles are metric by law worldwide. A 750 mL bottle is 0.1981290 US gallons and 25.3605170 fluid ounces, so five wine bottles are just short of one US gallon at 0.9906452 gallons. A standard 12 ounce can holds 354.8823548 mL, and nine cans hold 0.8437 gallons, a number worth knowing when a cooler is rated in quarts.

Small containers under one gallon

Everything below a gallon converts from the same three numbers, 0.2641720524 gallons, 33.8140227 fluid ounces and 4.2267528 cups per liter:

The table also covers the containers in a garage or a pantry. A 5 gallon jerry can holds 18.92705892 liters, so it takes 18.93 of the one liter bottles to fill one, and a 20 liter fuel can for a mower holds 5.2834410 gallons. In the kitchen, a 10 quart stock pot is 9.46352946 liters, and a 12 cup mixing bowl is 2.8390588 liters, so a liter of milk fills it to about 35 percent.

Reading the table backwards: the 1 quart milk carton is 946.352946 mL, a hair under a liter, and the 5 liter jug of water is 1.3208603 gallons, a bit past the 1 gallon jug beside it on the shelf. Whenever a label mixes the two systems, this table is the whole bridge.

Why the imperial gallon changes the answer

The UK and Canada still quote fuel economy and some drink volumes in imperial gallons, and the imperial gallon is 4.54609 liters, about 20 percent larger than the US gallon. One liter is 0.2199692 imperial gallons. That difference rewrites fuel numbers: 40 miles per US gallon is 33.31 miles per imperial gallon, so a UK spec sheet showing 33 mpg is describing the same car a US sheet shows at 40 mpg.

The mismatch also bites at import shops. A UK recipe asking for half an imperial gallon of stock wants 2.273045 liters, while a US cook pouring half a US gallon adds 1.892705892 liters. Between the two gallons the gap is 0.380339108 liters, more than a cup and a half, which is a real difference in a soup. Always check which gallon the source means before multiplying.

Reading a label that prints liters and ounces together

Mixed unit labels are common and easy to verify once you know the exact constants. One US fluid ounce is 29.5735295625 mL, so a 16.9 fl oz bottle holds 499.7926496 mL and the label's "500 mL" is a one decimal rounding. A 12 fl oz can holds 354.8823548 mL, and a 33.8 fl oz carton holds 999.5852992 mL, just under the liter it is sold as.

The same test works for the fuel cans sold in the same aisle. A can marked "5 L" holds 5 liters, which is 1.3208603 gallons, and a can marked "2.5 gal" holds 9.46352946 liters, so the metric can is the bigger one. If the two markings on the same can say 5 L and 1.3 gal, they agree to within rounding and you can use either number.

When the two numbers on a label disagree beyond one decimal of rounding, trust the milliliters. Metric values are legally exact on US labels while the ounce figure is rounded for display, so multiplying the printed mL by 0.2641720524 gives the gallons more faithfully than multiplying the printed ounces. The same rule holds for quarts: a 1.05 quart carton prints 1,000 mL, and 1,000 mL is the exact liter.

Case sizes and bulk buys in gallons

Wholesale packs turn one liter into gallon totals fast, and the numbers are useful when a recipe, a stock pot or a cooler has a gallon rating. Six 1 liter bottles are 1.5850323144 gallons, just over one and a half gallons. Twelve 1 liter bottles are 3.1700646288 gallons. A 24 pack of 500 mL bottles totals 12 liters, the same 3.1700646288 gallons, and six 2 liter bottles also land on 3.1700646288 gallons because they hold 12 liters too.

The wine case row is handy at parties: a standard 12 bottle case of 750 mL pours 9 liters, which is 2.3775484716 gallons, or about 19 bottles of the 16.9 fluid ounce water bottles by volume.