How do you convert liters to gallons?
Short answer. Divide liters by 3.785411784 for US gallons, or multiply by 0.264172. So 10 L is 2.64 US gal and 20 L is 5.28. For UK (imperial) gallons, divide by 4.54609 instead: 10 L is 2.20 UK gal. In reverse, multiply: 5 US gal is 18.93 L, and 5 UK gal is 22.73 L.
There are two gallons, and both are definitions rather than measurements. The US gallon is 231 cubic inches. Since 1959 an inch has been exactly 2.54 cm, so:
1 cubic inch = 2.54 × 2.54 × 2.54 = 16.387064 cm³ 1 US gallon = 231 × 16.387064 cm³ = 3785.411784 cm³ = 3.785411784 L 1 UK gallon = 4.54609 L exactly, by statute
Nine decimal places for the American one, five for the British one, and no rounding in either. Going back the other way is less tidy. As a fraction, a liter is 125000000/473176473 US gallons, and 473176473 is 3 × 7 × 11 × 127 × 127 × 127. The 3 × 7 × 11 is the 231, the three 127s are the inch (2.54 is 127/50) cubed, and none of them divides into a power of ten, so the decimal never ends: 0.2641720523581484 and on.
The two directions
Liters to US gallons: divide by 3.785411784. A 20 liter jerry can:
20 ÷ 3.785411784 = 5.283441047… → 5.28 US gal
US gallons to liters: multiply by 3.785411784. A 15 gallon fuel tank:
15 × 3.785411784 = 56.78117676 L exact, no rounding needed
Multiplying by 0.264172 instead of dividing by 3.785411784 lands in the same place: 20 × 0.264172 is 5.28344. That factor is itself rounded, so it is a shortcut, not an equal sign, but the gap only shows up in the sixth decimal place.
US gallon or UK gallon?
The imperial gallon is the bigger one, by about a fifth:
1 UK gallon = 4.54609 ÷ 3.785411784 = 1.20095 US gallons 1 US gallon = 3.785411784 ÷ 4.54609 = 0.83267 UK gallons
US recipes, US fuel prices and the American milk jug use the US gallon. Britain sells fuel by the liter but still quotes fuel economy in miles per imperial gallon, which is why the same car looks thriftier on a British spec sheet: 30 miles per US gallon is 30 × 1.20095 = 36.03 miles per UK gallon. Same car, same fuel, bigger gallon. The mpg post has the rest of that conversion.
A 55 liter car tank shows how far apart the answers are:
55 ÷ 3.785411784 = 14.5294… → 14.53 US gal 55 ÷ 4.54609 = 12.0983… → 12.10 UK gal
If a source just says "gallons" and it is American, assume US. If it is British and about cars, assume imperial. If it is a recipe on the internet, check where the author lives.
A liter is a little more than a quart
A US quart is a quarter of a US gallon, exactly 0.946352946 L. So one liter is 1 ÷ 0.946352946 = 1.05669 quarts. That is the whole reason "about a quarter of a gallon" undershoots: a liter is a quarter gallon plus about five and two thirds percent.
The 2 liter soda bottle is the everyday proof. Half a US gallon is 1.892705892 L, so the bottle holds 2 − 1.892705892 = 0.107294108 L more, which is 107.3 mL, a bit under half a cup. In gallons the bottle is 0.5283.
Doing it in your head: a quarter, plus five percent
Quarter the liters, then add five percent of the result. That is multiplying by 0.2625 against a true 0.264172:
20 L → 20 ÷ 4 = 5 → 5 + 0.25 = 5.25 US gal Exact 20 ÷ 3.785411784 = 5.2834… 100 L → 100 ÷ 4 = 25 → 25 + 1.25 = 26.25 US gal Exact 100 ÷ 3.785411784 = 26.4172…
The estimate always runs low by the same proportion, 0.63%. Plain quartering, with no five percent, is 5.36% low, which on a 100 liter tank loses 1.42 gallons.
The other way, multiply the gallons by four and take off five percent. That is multiplying by 3.8, which runs 0.39% high: 10 US gallons gives 40 − 2 = 38 L against a true 37.85 L, and 5 gallons gives 20 − 1 = 19 L against 18.93 L.
Conversion table: liters to gallons
| Liters | US gallons | UK gallons |
|---|---|---|
| 1 | 0.264 | 0.220 |
| 2 | 0.528 | 0.440 |
| 4 | 1.057 | 0.880 |
| 5 | 1.321 | 1.100 |
| 10 | 2.642 | 2.200 |
| 20 | 5.283 | 4.399 |
| 25 | 6.604 | 5.499 |
| 50 | 13.209 | 10.998 |
| 55 | 14.529 | 12.098 |
| 60 | 15.850 | 13.198 |
| 100 | 26.417 | 21.997 |
| 200 | 52.834 | 43.994 |
| 1000 | 264.172 | 219.969 |
The last row is a cubic meter. It holds 264 US gallons, which is a useful number to have when someone quotes a pool or a water tank in one unit and the pump in the other.
Conversion table: gallons to liters
Every row here is exact. Multiplying a whole number of gallons by 3.785411784 or 4.54609 never needs more decimal places than the factor has, so there is nothing to round:
| Gallons | US gallons to liters | UK gallons to liters |
|---|---|---|
| 1 | 3.785411784 | 4.54609 |
| 2 | 7.570823568 | 9.09218 |
| 3 | 11.356235352 | 13.63827 |
| 5 | 18.92705892 | 22.73045 |
| 10 | 37.85411784 | 45.4609 |
| 12 | 45.424941408 | 54.55308 |
| 15 | 56.78117676 | 68.19135 |
| 20 | 75.70823568 | 90.9218 |
| 50 | 189.2705892 | 227.3045 |
| 100 | 378.5411784 | 454.609 |
Where the rounded factor costs you
On 100 liters, each popular shortcut against the exact answer:
Exact 100 ÷ 3.785411784 = 26.4172052… US gal 0.264172 100 × 0.264172 = 26.4172 US gal short by 0.0000052 gal 0.26 100 × 0.26 = 26 US gal short by 0.42 gal ÷ 4 100 ÷ 4 = 25 US gal short by 1.42 gal
So 0.264172 is good for anything, 0.26 is good for a bucket, and dividing by four is good for an argument.
The binary arithmetic underneath has its own opinion. Three US gallons is 3 × 3.785411784, which is 11.356235352 L and nothing else. A machine working in binary floating point answers 11.356235351999999, because 3.785411784 has no exact binary form. That trailing run of nines is the same fault behind 0.1 + 0.2 = 0.30000000000000004, and it is why chained conversions drift. Prism holds 3.785411784 as the exact number it is, so 3 gallons converts to 11.356235352 L, and 0.1 + 0.2 is 0.3. The same goes for weight, where a pound is exactly 0.45359237 kg, as the kg to lbs post works through.
Divide it, or let the converter hold both gallons
Dividing by 3.785411784 works in Prism's free calculator, exactly. The volume category of the unit converter (liters, milliliters, US and UK gallons, quarts, pints, cups, fluid ounces, tablespoons, teaspoons and cubic meters) is part of the one-time $3.99 unlock. No ads, no subscription. See the app.