Gallons to Milliliters
Source: NIST SP 811 Appendix B.9 and NIST Handbook 44 Appendix C for the US liquid gallon, and the Weights and Measures Act 1985 Schedule 1 for the Imperial gallon · Source verified August 14, 2026
A volume conversion tool that turns gallons into milliliters. One US liquid gallon is exactly 3,785.411784 milliliters and one Imperial gallon is exactly 4,546.09 milliliters, both following from statutory definitions rather than measurement.
Start with a figure in gallons and read it back in milliliters. Pick the US liquid or Imperial gallon, and the formula, the working, and the reference table all follow your choice.
Quick Answer
Multiply gallons by 3,785.411784 for US liquid, or by 4,546.09 for Imperial. For example, 2 US gallons is 7,570.82 mL.
Gallon standard
1 US liquid gallon = 3.785411784 liters. The Imperial gallon is about 20% larger than the US one, so switching changes every figure below.
Answer in milliliters
18,927.1 mL
5 gal × 3,785.41 = 18,927.1 mL
5 US liquid gallons is 18,927.1 milliliters.
The unit relationships are exact by definition. The calculator derives this factor from those definitions, runs the calculation in double-precision floating point, and rounds the displayed result to six significant digits.
Entered: 5 gal
Examples
0.25 gal
= 946.35 mL
0.50 gal
= 1,892.71 mL
1 gal
= 3,785.41 mL
2 gal
= 7,570.82 mL
How it works
Formula · US liquid: mL = gal × 3,785.411784 · Imperial: mL = gal × 4,546.09
This conversion multiplies by a large number, because a milliliter is a very small unit next to a gallon. Expect answers in the thousands.
US liquid gallon
mL = gal × 3,785.411784
Imperial (UK) gallon
mL = gal × 4,546.09
Both factors come from definitions rather than measurement. The US liquid gallon is 231 cubic inches and the Imperial gallon is 4.54609 liters, both fixed by the standards cited below. Shorter decimals you may see elsewhere are these same values rounded.
Which gallon do you mean?
“Gallon” is not one unit. The two in common use differ by about 20%, which is far too much to ignore:
- US liquid gallon, 3.785411784 liters. The default here, and what United States fuel, beverage, and recipe figures mean.
- Imperial gallon, 4.54609 liters. About 20% larger. Used in the United Kingdom and parts of the Commonwealth.
There is also a US dry gallon, a separate unit for dry goods that this page does not convert. If a figure came from a fuel pump, a drinks label, or a recipe, it is a liquid gallon.
Gallons to Milliliters reference table
Converted columns are rounded for display, so they are equivalents rather than exact statements. Both gallon standards are shown side by side.
| Gallons | US liquid (mL) | Imperial (mL) | Note |
|---|---|---|---|
| 0.25 gal | 946.35 mL | 1,136.52 mL | |
| 0.50 gal | 1,892.71 mL | 2,273.05 mL | Half a gallon |
| 1 gal | 3,785.41 mL | 4,546.09 mL | One gallon |
| 2 gal | 7,570.82 mL | 9,092.18 mL | |
| 5 gal | 18,927.06 mL | 22,730.45 mL | |
| 10 gal | 37,854.12 mL | 45,460.90 mL | |
| 20 gal | 75,708.24 mL | 90,921.80 mL |
Common mistakes
- Using the wrong gallon. 1 US gallon is 3,785.41 mL while 1 Imperial gallon is 4,546.09 mL.
- Confusing milliliters with liters. Multiply by 3,785.411784 for milliliters, not by 3.785411784.
- Treating 3,800 mL as a gallon. It is close but not the same, and the gap compounds across several gallons.
Sources
- NIST Special Publication 811, Appendix B.9, which gives the inch as exactly 2.54 cm. Cubing that gives the cubic inch as exactly 16.387064 cm³.
- NIST Handbook 44, Appendix C, which defines the US liquid gallon as 231 cubic inches. With the inch above that fixes the US gallon at exactly 3.785411784 liters.
- Weights and Measures Act 1985, Schedule 1, which defines the Imperial gallon as 4.54609 cubic decimetres, that is 4.54609 liters.
These relationships are exact as definitions. The calculator derives its factor from them, computes in double-precision floating point, and rounds what it displays.
Related converters
- Milliliters to gallons for the reverse, when your figure is metric.
- Gallons to liters when liters suit the scale better than milliliters.
- Fluid ounces to milliliters for a smaller US customary unit.
- Volume converter for cups, pints, quarts, cubic units, and more.
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