Short answer
- A US gallon contains 3,785.41 milliliters. An imperial gallon contains 4,546.09 milliliters. Those are the two correct answers, and the right one depends entirely on which gallon you mean. | Gallon | Fluid ounces | Liters | Milliliters | |---|---|---|---| | US gallon | 128 US fluid ounces | 3.78541 liters | 3,785.41 milliliters | | Imperial gallon | 160 imperial fluid ounces | 4.54609 liters | 4,546.09 milliliters | The exact basis behind the rounded figures in that table is 3,785.411784 milliliters for one US gallon and exactly 4,546.09 milliliters for one imperial gallon. The imperial gallon is larger by 760.68 milliliters, which is roughly three quarters of a liter, so the two answers are never interchangeable. An imperial gallon is about 20.1 percent larger than a US gallon. If a source just says "a gallon" without naming the system, check where the source comes from. American sources almost always mean the US gallon, because that is the gallon used for fuel, milk, paint, and packaged liquids in the United States. British sources, and fuel economy figures quoted in miles per gallon in the United Kingdom, mean the imperial gallon. Naming the system first is the single most important step in every conversion in this article.
By Emma Hudson
How many milliliters are in a gallon sounds like a question with one answer. It has two, because there are two gallons in everyday use, and they are different sizes. This guide gives both answers, shows where each figure comes from, and provides full tables and worked examples so you can convert in either direction without mixing the two systems up.
The Two Gallons and Where Their Sizes Come From
The US liquid gallon is defined as exactly 231 cubic inches. Because one inch is exactly 2.54 centimeters, one cubic inch is exactly 16.387064 cubic centimeters, and 231 multiplied by 16.387064 gives 3,785.411784 cubic centimeters. A cubic centimeter is the same volume as a milliliter, so one US gallon is exactly 3,785.411784 milliliters, which is 3.785411784 liters. Most tables round that to 3,785.41 milliliters, and that rounding is close enough for almost every purpose, as long as you round at the end of a calculation rather than at the start.
The imperial gallon is defined directly in metric terms as exactly 4.54609 cubic decimeters. A cubic decimeter is one liter, so one imperial gallon is exactly 4.54609 liters, or 4,546.09 milliliters. That definition is set in the United Kingdom Weights and Measures Act 1985, Schedule 1, which also defines the imperial quart as one quarter of a gallon, the imperial pint as half a quart, and the imperial fluid ounce as one twentieth of a pint.
The two gallons come from different historical definitions, which is why they differ. The US gallon descends from the older English wine gallon of 231 cubic inches, which the American colonies kept. Britain replaced its older gallons in 1824 with the imperial gallon, based on the volume of ten pounds of water under stated conditions, and later restated that gallon in exact metric terms. Neither country adopted the other’s gallon, so both survive side by side, and a conversion that does not say which one it uses is incomplete.
A milliliter, for reference, is one thousandth of a liter, and a liter is one cubic decimeter. That simple relationship is a useful cross-check on every figure in this article: the milliliter value of any gallon must be exactly one thousand times its liter value. If a table ever shows a gallon as 3.785 liters and 3,758 milliliters, one of the two figures is wrong.
How the Figures Are Worked Out From Fluid Ounces
Both gallon systems can also be built up from their fluid ounces, and doing the working once shows why the two systems must never be mixed mid-calculation.
US gallon:
- 1 US gallon = 128 US fluid ounces
- 1 US fluid ounce = 29.5735 milliliters (exactly 29.5735295625 milliliters)
- 128 × 29.5735295625 = 3,785.411784 milliliters, rounded to 3,785.41 milliliters
Imperial gallon:
- 1 imperial gallon = 160 imperial fluid ounces
- 1 imperial fluid ounce = 28.4131 milliliters (exactly 28.4130625 milliliters)
- 160 × 28.4130625 = 4,546.09 milliliters exactly
Two things are happening at once. The imperial gallon contains more fluid ounces, 160 against 128. But each imperial fluid ounce is slightly smaller than a US fluid ounce, 28.4131 milliliters against 29.5735 milliliters. The larger ounce count wins, so the imperial gallon still comes out larger overall, by 760.68 milliliters.
Both steps matter. If you multiplied the imperial ounce count by the US ounce size, 160 × 29.5735, you would get 4,731.76 milliliters, which matches neither gallon and is wrong by more than 185 milliliters against the imperial figure. Always pair each system’s ounce count with that same system’s ounce size.
Conversion Formulas
Gallons to milliliters:
- US: milliliters = US gallons × 3,785.411784
- Imperial: milliliters = imperial gallons × 4,546.09
Milliliters to gallons:
- US: US gallons = milliliters ÷ 3,785.411784
- Imperial: imperial gallons = milliliters ÷ 4,546.09
Liters to gallons, for the same conversions stated in liters:
- US: US gallons = liters ÷ 3.785411784, so 1 liter = 0.264172 US gallons
- Imperial: imperial gallons = liters ÷ 4.54609, so 1 liter = 0.219969 imperial gallons
For rough everyday planning, 3,800 milliliters per US gallon and 4,550 milliliters per imperial gallon are close enough. For fuel, brewing, chemistry, medication-adjacent measuring, aquarium treatments, or anything where a few percent matters, use the full figures and round only the final answer.
US Gallons to Milliliters
Every value in this table is calculated from the exact basis of 3,785.411784 milliliters per US gallon and then rounded to two decimal places.
| US gallons | Milliliters | Liters |
|---|---|---|
| 0.25 (1 quart) | 946.35 | 0.946 |
| 0.5 (half gallon) | 1,892.71 | 1.893 |
| 0.75 | 2,839.06 | 2.839 |
| 1 | 3,785.41 | 3.785 |
| 1.5 | 5,678.12 | 5.678 |
| 2 | 7,570.82 | 7.571 |
| 2.5 | 9,463.53 | 9.464 |
| 3 | 11,356.24 | 11.356 |
| 4 | 15,141.65 | 15.142 |
| 5 | 18,927.06 | 18.927 |
| 6 | 22,712.47 | 22.712 |
| 7 | 26,497.88 | 26.498 |
| 8 | 30,283.29 | 30.283 |
| 9 | 34,068.71 | 34.069 |
| 10 | 37,854.12 | 37.854 |
| 15 | 56,781.18 | 56.781 |
| 20 | 75,708.24 | 75.708 |
| 25 | 94,635.29 | 94.635 |
| 50 | 189,270.59 | 189.271 |
| 100 | 378,541.18 | 378.541 |
Check the working for 2 US gallons: 2 × 3,785.411784 = 7,570.823568 milliliters, which rounds to 7,570.82 milliliters. Half a US gallon is 1,892.71 milliliters, and it is also 64 US fluid ounces, a figure you may recognize from half gallon milk and juice containers in the United States. A quarter of a US gallon is one US quart, at 946.35 milliliters, just under one liter.
Imperial Gallons to Milliliters
Every value in this table is calculated from exactly 4,546.09 milliliters per imperial gallon.
| Imperial gallons | Milliliters | Liters |
|---|---|---|
| 0.25 (1 imperial quart) | 1,136.52 | 1.137 |
| 0.5 (half imperial gallon) | 2,273.05 | 2.273 |
| 0.75 | 3,409.57 | 3.410 |
| 1 | 4,546.09 | 4.546 |
| 1.5 | 6,819.14 | 6.819 |
| 2 | 9,092.18 | 9.092 |
| 2.5 | 11,365.23 | 11.365 |
| 3 | 13,638.27 | 13.638 |
| 4 | 18,184.36 | 18.184 |
| 5 | 22,730.45 | 22.730 |
| 6 | 27,276.54 | 27.277 |
| 7 | 31,822.63 | 31.823 |
| 8 | 36,368.72 | 36.369 |
| 9 | 40,914.81 | 40.915 |
| 10 | 45,460.90 | 45.461 |
| 15 | 68,191.35 | 68.191 |
| 20 | 90,921.80 | 90.922 |
| 25 | 113,652.25 | 113.652 |
| 50 | 227,304.50 | 227.305 |
| 100 | 454,609.00 | 454.609 |
Check the working for 3 imperial gallons: 3 × 4,546.09 = 13,638.27 milliliters. A quarter of an imperial gallon, one imperial quart, is 1,136.52 milliliters, which is also 40 imperial fluid ounces. Notice that even the imperial quart is larger than a full liter, while the US quart is slightly smaller than a liter. That one comparison explains a great deal of confusion when recipes and container sizes cross the Atlantic.
Milliliters Back to Gallons
| Milliliters | US gallons | Imperial gallons |
|---|---|---|
| 250 | 0.066 | 0.055 |
| 500 | 0.132 | 0.110 |
| 750 | 0.198 | 0.165 |
| 1,000 (1 liter) | 0.264 | 0.220 |
| 1,500 | 0.396 | 0.330 |
| 2,000 | 0.528 | 0.440 |
| 2,500 | 0.660 | 0.550 |
| 3,000 | 0.793 | 0.660 |
| 3,785.41 | 1.000 | 0.833 |
| 4,000 | 1.057 | 0.880 |
| 4,546.09 | 1.201 | 1.000 |
| 5,000 | 1.321 | 1.100 |
| 7,500 | 1.981 | 1.650 |
| 10,000 | 2.642 | 2.200 |
| 20,000 | 5.283 | 4.399 |
Check the working for 5,000 milliliters in US gallons: 5,000 ÷ 3,785.411784 = 1.321 US gallons. The same 5,000 milliliters in imperial gallons is 5,000 ÷ 4,546.09 = 1.100 imperial gallons. Same volume, two different gallon counts, which is exactly why the system must be named before the arithmetic starts. The table also shows the cleanest illustration of the size gap: 3,785.41 milliliters is a full US gallon but only 0.833 of an imperial gallon, and 4,546.09 milliliters is a full imperial gallon but 1.201 US gallons.
Fractions of a Gallon in Milliliters
Recipes, dosing instructions, and mixing guides often call for a fraction of a gallon rather than a whole number. These are the fractions you are most likely to meet.
| Fraction of a gallon | US milliliters | Imperial milliliters |
|---|---|---|
| One sixteenth | 236.59 | 284.13 |
| One eighth | 473.18 | 568.26 |
| One quarter | 946.35 | 1,136.52 |
| One third | 1,261.80 | 1,515.36 |
| One half | 1,892.71 | 2,273.05 |
| Two thirds | 2,523.61 | 3,030.73 |
| Three quarters | 2,839.06 | 3,409.57 |
| One full gallon | 3,785.41 | 4,546.09 |
The fractions connect directly to the smaller units in each system. One sixteenth of a US gallon is one US cup, at 236.59 milliliters. One eighth of a US gallon is one US pint, at 473.18 milliliters. One eighth of an imperial gallon is one imperial pint, at 568.26 milliliters, which is why a British pint of beer or milk is noticeably larger than an American pint. One third of a gallon has no named unit in either system, so it has to be calculated: one third of 3,785.411784 is 1,261.80 milliliters, and one third of 4,546.09 is 1,515.36 milliliters.
Quarts, Pints, Cups, and Fluid Ounces in Milliliters
Because the gallon sits at the top of each liquid measurement chain, its milliliter value cascades down through every smaller unit.
US liquid system:
- 1 US gallon = 3,785.41 milliliters
- 1 US quart = 946.35 milliliters (one quarter of a gallon: 3,785.411784 ÷ 4 = 946.352946)
- 1 US pint = 473.18 milliliters (one eighth of a gallon: 3,785.411784 ÷ 8 = 473.176473)
- 1 US cup = 236.59 milliliters (one sixteenth of a gallon: 3,785.411784 ÷ 16 = 236.588237)
- 1 US tablespoon = 14.79 milliliters
- 1 US teaspoon = 4.93 milliliters
- 1 US fluid ounce = 29.57 milliliters (exactly 29.5735295625 milliliters)
Imperial system:
- 1 imperial gallon = 4,546.09 milliliters
- 1 imperial quart = 1,136.52 milliliters (one quarter of a gallon)
- 1 imperial pint = 568.26 milliliters (one eighth of a gallon: 4,546.09 ÷ 8 = 568.26125)
- 1 imperial fluid ounce = 28.41 milliliters (exactly 28.4130625 milliliters)
The structure of the two chains differs, and the difference matters in recipes. A US pint holds 16 US fluid ounces, because a US fluid ounce is one eighth of a US cup and a pint is two cups. An imperial pint holds 20 imperial fluid ounces, because the imperial fluid ounce is defined as one twentieth of an imperial pint. So “a pint” and “an ounce” both change size when the system changes, and a recipe that gives one ingredient in pints and another in fluid ounces only works if all of its units come from the same system. There is no single imperial cup in the legal imperial chain, which is why British recipes usually give liquids in milliliters, liters, pints, or fluid ounces rather than cups.
The US Dry Gallon
The United States also has a dry gallon, used historically for dry goods such as grain and produce rather than for liquids. One US dry gallon is one eighth of a US bushel and equals 4.40488377086 liters, which is 4,404.88 milliliters. That places it between the US liquid gallon at 3,785.41 milliliters and the imperial gallon at 4,546.09 milliliters, at about 16.4 percent larger than the US liquid gallon.
You will almost never need the dry gallon. It does not appear on fuel pumps, milk containers, paint cans, or aquarium products, and modern American dry goods are usually sold by weight or by the bushel and peck rather than by the dry gallon. Unless a source explicitly says “dry gallon,” assume it means the liquid gallon for anything that pours. The note is included here only so that, if you meet the term in an older agricultural or historical source, you know it is a third, different size and not a misprint of either liquid gallon.
Where Each Gallon Is Used
The US gallon is the standard gallon in the United States for fuel, milk, paint, water heaters, aquariums, and most consumer liquids. If you buy a gallon of milk in an American supermarket, it holds 3,785.41 milliliters. If an American car has a 12 gallon fuel tank, that tank holds 12 × 3,785.411784 = 45,424.94 milliliters, or about 45.42 liters.
The imperial gallon survives in the United Kingdom and some Commonwealth countries, most visibly in fuel economy figures quoted in miles per imperial gallon, and in some older plumbing, brewing, and bulk liquid contexts. Everyday retail liquids in the United Kingdom are sold in liters and milliliters, so the imperial gallon now appears mainly in miles per gallon ratings, in older documents, and in comparisons imported from British sources.
That survival creates a well known trap in fuel economy comparisons. A car rated at 40 miles per gallon in the United Kingdom is not directly comparable to a car rated at 40 miles per gallon in the United States, because the British gallon is about 20.1 percent larger, so the British car travels those 40 miles on more fuel. Converted to the same gallon, 40 miles per imperial gallon equals 40 × 3,785.411784 ÷ 4,546.09 = 33.31 miles per US gallon. Anyone who compares the two headline figures without converting is comparing different sized gallons and will think the British rated car is more efficient than it is on a like for like basis.
The same trap appears in aquariums, where American tank sizes are given in US gallons and some British and international guides give volumes in liters, and in home brewing, where older British recipes use imperial gallons and American recipes use US gallons. A five gallon batch means 18,927.06 milliliters in an American recipe and 22,730.45 milliliters in an imperial one, a difference of more than 3,800 milliliters, which is more than a whole extra US gallon of liquid. That is far too large a difference to absorb as a rounding error.
Worked Examples
A 5 liter container in US gallons. 5 liters is 5,000 milliliters. Dividing by 3,785.411784 gives 1.321 US gallons, so a 5 liter container is about a third larger than a US gallon jug.
A 5 liter container in imperial gallons. The same 5,000 milliliters divided by 4,546.09 gives 1.100 imperial gallons, so the same container is only about a tenth larger than an imperial gallon.
Filling a 10 gallon tank in milliliters. In US gallons, 10 × 3,785.411784 = 37,854.12 milliliters, or about 37.85 liters. A tank marked 10 imperial gallons would need 45,460.90 milliliters instead, a difference of 7,606.78 milliliters, which is over 7.6 liters, for the same words “10 gallons.”
A 20 US gallon aquarium. 20 × 3,785.411784 = 75,708.24 milliliters, or about 75.71 liters. A 55 US gallon aquarium holds 208,197.65 milliliters, or about 208.20 liters. These figures matter when a water treatment or medication is dosed per liter: the dose has to be calculated from the liter figure, not from a guessed conversion of the gallon figure.
A cleaning mix at 30 milliliters per liter. Suppose a cleaning concentrate is diluted at 30 milliliters of concentrate per liter of water, and you are filling a US gallon sprayer. One US gallon is 3.785411784 liters, so the concentrate needed is 30 × 3.785411784 = 113.56 milliliters, in a total mix of 3,785.41 milliliters. If you used the imperial figure by mistake, you would add 30 × 4.54609 = 136.38 milliliters, making the mix about 20 percent stronger than intended. Ratio mixes are where a gallon mix up stops being an abstract error and starts changing the strength of what you spray, soak, or apply.
Scaling a recipe from cups to a gallon batch. A US cup is 236.59 milliliters, and there are 16 cups in a US gallon. A soup recipe that makes 4 cups, about 946.35 milliliters, scales to a full US gallon batch by multiplying every ingredient by four, giving 3,785.41 milliliters in total. If the same recipe were scaled using an imperial gallon as the target, the batch would come out at 4,546.09 milliliters and every ingredient would need multiplying by about 4.8 instead of 4, which would overflow a gallon container bought in the United States.
Half a gallon of paint. Half a US gallon is 1,892.71 milliliters, just under 2 liters. Half an imperial gallon is 2,273.05 milliliters, well over 2 liters. Paint coverage is calculated per volume, so buying or mixing paint by the half gallon without knowing the system can leave a room under coated or a tin mostly unused.
Bottles into gallons. A standard 750 milliliter bottle is 0.198 US gallons and 0.165 imperial gallons. It takes 5.05 such bottles to make a US gallon and 6.06 to make an imperial gallon. A 500 milliliter bottle is 0.132 US gallons, and it takes 7.57 of them to fill a US gallon, against 9.09 to fill an imperial gallon.
Rounding and Precision
Most everyday conversions only need the two decimal place figures used in the tables: 3,785.41 and 4,546.09. The error introduced by using 3,785.41 instead of the exact 3,785.411784 is less than two thousandths of a milliliter per gallon, which no kitchen jug, fuel pump display, or aquarium measure can detect.
Rounding becomes a real problem in two situations. The first is rounding the conversion factor itself to a whole number. Using 3,800 milliliters per US gallon overstates one gallon by about 14.59 milliliters, which is harmless, but over 50 gallons the same shortcut overstates the total by about 729 milliliters. The second is rounding intermediate steps in a chain, for example converting gallons to fluid ounces, rounding, then converting ounces to milliliters. Keep full precision through the calculation and round only the final answer, and chained conversions will match the direct tables in this article.
Common Mistakes
- Using 3,785.41 milliliters for an imperial gallon. This understates an imperial gallon by 760.68 milliliters, an error of about 16.7 percent of the imperial gallon.
- Using 4,546.09 milliliters for a US gallon. This overstates a US gallon by the same 760.68 milliliters, an error of about 20.1 percent of the US gallon.
- Multiplying imperial ounces by the US ounce size. 160 × 29.5735 = 4,731.76 milliliters matches neither gallon. Always pair each system’s ounce count with its own ounce size.
- Assuming a gallon is 4 liters. A US gallon is 3.78541 liters, about 5.4 percent short of 4 liters. An imperial gallon is 4.54609 liters, about 13.7 percent over 4 liters. Four liters is 4,000 milliliters, which is 1.057 US gallons and 0.880 imperial gallons, so it is not a gallon in either system.
- Rounding too early. Rounding 3,785.41 to 3,800 is fine for one gallon, but multiplied by 50 the rounding error grows to nearly 730 milliliters. Round the answer, not the factor.
- Confusing fluid ounces with weight ounces. A fluid ounce measures volume and a weight ounce measures mass. This article is only about volume. The weight of a gallon depends on what liquid fills it.
- Confusing the dry gallon with the liquid gallon. The US dry gallon, at about 4.405 liters, is a third size again. Unless a source explicitly says dry gallon, use the liquid gallon for liquids.
Frequently Asked Questions
How many milliliters are in a gallon of water?
A US gallon of water is 3,785.41 milliliters, and an imperial gallon of water is 4,546.09 milliliters. The liquid does not change the conversion, because a gallon is a volume, so water, milk, and fuel all convert the same way. What changes with the liquid is the weight. A US gallon of water weighs about 8.3 pounds, while a US gallon of a denser liquid weighs more.
How many milliliters are in half a gallon?
Half a US gallon is 1,892.71 milliliters. Half an imperial gallon is 2,273.05 milliliters.
How many milliliters are in a quarter of a gallon?
A quarter of a US gallon is one US quart, at 946.35 milliliters. A quarter of an imperial gallon is one imperial quart, at 1,136.52 milliliters.
Is a gallon 4 liters?
No, although it is close enough that the approximation causes trouble. A US gallon is 3.78541 liters, which is about 5.4 percent short of 4 liters. An imperial gallon is 4.54609 liters, which is about 13.7 percent over 4 liters. For rough shopping, “about 4 liters” is a usable picture of a US gallon. For anything measured, use the exact figure for the system you are working in.
How many 500 milliliter bottles fill a gallon?
A US gallon needs 3,785.411784 ÷ 500 = 7.57 bottles, so seven full bottles plus a bit more than half of another. An imperial gallon needs 4,546.09 ÷ 500 = 9.09 bottles, so nine full bottles plus a small part of another.
How many milliliters are in 2 gallons?
Two US gallons are 7,570.82 milliliters. Two imperial gallons are 9,092.18 milliliters.
How many milliliters are in 5 gallons?
Five US gallons are 18,927.06 milliliters. Five imperial gallons are 22,730.45 milliliters.
How do you convert milliliters to gallons?
Divide the milliliter figure by the conversion factor for your system. For US gallons, divide by 3,785.411784. For imperial gallons, divide by 4,546.09. For example, 10,000 milliliters is 2.642 US gallons and 2.200 imperial gallons.
Why is the imperial gallon bigger?
The two gallons come from different historical definitions. The US gallon descends from an older English wine gallon of 231 cubic inches, while the imperial gallon was standardized in Britain in 1824 and is now defined as exactly 4.54609 liters. The two definitions simply produce different sizes, and both survived because each country kept its own system after the definitions diverged.
Which gallon should I use?
Use the gallon of the country and context your source comes from. Use the US gallon for American recipes, American fuel and container sizes, and American aquarium and paint products. Use the imperial gallon for British miles per gallon figures and for older British and Commonwealth sources that specify imperial measure. If a modern source gives volumes in liters or milliliters, work in liters and milliliters and skip the gallon conversion entirely.
Keep reading: How Many Ounces in a Gallon
Keep reading: Liters to Gallons: How Many Liters in a Gallon?
Keep reading: Ounces in a Pint: The US, UK, and Dry Pint, Explained
Keep reading: Liters to Ounces: Exact Conversion Table & Examples
Sources & references
- National Institute of Standards and Technology (NIST), Metric Kitchen: Cooking Measurement Equivalencies. Used for the US customary liquid chain in home measurement: 1 gallon = 4 quarts = 128 fluid ounces = 16 cups, 1/2 gallon = 64 fluid ounces = 8 cups, 1 quart = 32 fluid ounces, 1 pint = 16 fluid ounces, and the approximate metric equivalents published on that page for cups, pints, quarts, and fluid ounces. https://www.nist.gov/pml/owm/metric-si/metric-kitchen/metric-kitchen-cooking-measurement-equivalencies
- United Kingdom, Weights and Measures Act 1985, Schedule 1, Definitions of Units of Measurement (as enacted), via legislation.gov.uk. Used for the imperial gallon defined as exactly 4.54609 cubic decimeters, the liter defined as a cubic decimeter, the milliliter defined as 1/1000 liter, the imperial quart as 1/4 gallon, the imperial pint as 1/2 quart, and the imperial fluid ounce as 1/20 pint. https://www.legislation.gov.uk/ukpga/1985/72/schedule/1/enacted/data.xml
- National Institute of Standards and Technology (NIST), Guide for the Use of the International System of Units, NIST Special Publication 811, Appendix B.8, and NIST Handbook 44, Appendix B and Appendix C conversion factors. Used for the US liquid gallon defined as exactly 231 cubic inches, equal to exactly 3.785411784 liters (3,785.411784 milliliters), the US fluid ounce as 1/128 of that gallon, and the US dry gallon as 1/8 of a US bushel, equal to 4.40488377086 liters. The exact factors were also recomputed from the definitions during writing: 231 × 16.387064 = 3,785.411784, 128 × 29.5735295625 = 3,785.411784, and 160 × 28.4130625 = 4,546.09. https://www.nist.gov/physical-measurement-laboratory/nist-guide-si-appendix-b8
