Two gallons, one liter
The liter is a special name for the cubic decimeter: a cube 10 cm on each side. A milliliter is a cubic centimeter, and a cubic meter holds 1,000 liters. Metric volumes therefore link directly to length, which is why the converter can include cubic inches and cubic feet alongside liters.
English-speaking countries ended up with two gallons that share a name but not a size:
- The US gallon is defined as 231 cubic inches. Since the inch is exactly 2.54 cm, that works out to exactly 3.785411784 L. It splits into 4 quarts, 8 pints and 128 US fluid ounces.
- The imperial gallon, set by UK law, is exactly 4.54609 L. It splits into 8 pints and 160 imperial fluid ounces.
The odd consequence is that the imperial gallon and pint are about 20% larger than their US namesakes, while the imperial fluid ounce (28.41 mL) is slightly smaller than the US one (29.57 mL). An imperial pint holds 20 of its fluid ounces; a US pint holds 16 of its own.
Volume formulas
Each factor is exact because it comes from a defined gallon or from the exact inch cubed. The working line under the result shows the factor for whichever pair you choose.
| Unit | Liters | Used in |
|---|---|---|
| Milliliter (mL) | 0.001 | Worldwide, drinks and medicine |
| Cubic inch (in³) | 0.016387064 | Older US engine sizes |
| US fluid ounce | 0.0295735295625 | US drink labels |
| Imperial fluid ounce | 0.0284130625 | UK, older recipes |
| US pint | 0.473176473 | US milk, ice cream |
| Imperial pint | 0.56826125 | UK and Ireland, draught beer and milk |
| US gallon | 3.785411784 | US fuel and milk |
| Imperial gallon | 4.54609 | UK fuel economy figures (mpg) |
| Cubic foot (ft³) | 28.316846592 | Appliance and room volumes in the US |
| Cubic meter (m³) | 1,000 | Water bills, freight, concrete |
Worked examples
- US gallons: 50 ÷ 3.785411784 = 13.2086 US gal.
- Imperial gallons: 50 ÷ 4.54609 = 10.9985 imp gal.
- The same tank sounds bigger in US gallons because the US gallon is the smaller unit.
- Multiply the inside dimensions: 60 × 30 × 30 = 54,000 cm³.
- A liter is 1,000 cm³, so the tank holds 54 L.
- Divide by the US gallon: 54 ÷ 3.785411784 = 14.2653 US gal.
- Multiply by the US fluid ounce: 12 × 29.5735295625 = 354.882 mL.
- Labels round this to 355 mL.
- Imperial pint: 568.26125 mL. US pint: 473.176473 mL.
- Divide: 568.26125 ÷ 473.176473 = 1.20095, so the imperial pint holds about 20.1% more.
Liters and gallons table
| Liters (L) | US gallons (US gal) | Imperial gallons (imp gal) |
|---|---|---|
| 1 | 0.264172 | 0.219969 |
| 2 | 0.528344 | 0.439938 |
| 4 | 1.05669 | 0.879877 |
| 5 | 1.32086 | 1.09985 |
| 10 | 2.64172 | 2.19969 |
| 20 | 5.28344 | 4.39938 |
| 40 | 10.5669 | 8.79877 |
| 50 | 13.2086 | 10.9985 |
| 60 | 15.8503 | 13.1982 |
| 100 | 26.4172 | 21.9969 |
| US gallons (US gal) | Liters (L) | Imperial gallons (imp gal) |
|---|---|---|
| 1 | 3.78541 | 0.832674 |
| 2 | 7.57082 | 1.66535 |
| 5 | 18.9271 | 4.16337 |
| 10 | 37.8541 | 8.32674 |
| 15 | 56.7812 | 12.4901 |
| 20 | 75.7082 | 16.6535 |
| 50 | 189.271 | 41.6337 |
Mistakes with gallons, pints and fluid ounces
- Assuming a gallon is a gallon. A UK car brochure quoting a tank in gallons means imperial gallons; a US one means US gallons. Pick the matching unit in the From select.
- Converting fluid ounces with the wrong pint in mind. 20 imperial fl oz make a UK pint, but those 20 ounces are only 19.2 US fl oz. Convert the ounces themselves, not the pint count.
- Mixing up liquid and dry measures. US customary units also include dry pints, dry quarts and bushels, which are different sizes again. This converter covers liquid measures only.
- Forgetting to cube the length factor. One cubic foot is 28.3 L, not 0.3048 m³; a foot is 0.3048 m but a cubic foot is 0.3048³ m³.
Cooking cups and spoons vary by country in ways that go beyond the US and imperial split. For recipes, the cooking measurement converter covers the US, legal, metric and Japanese cups.
Questions people ask
How many liters are in a gallon?
3.785 L in a US gallon and 4.546 L in an imperial gallon. Both figures come from exact definitions.
Is a liter more than a quart?
Slightly. A US liquid quart is 0.946 L, so a liter is about 1.057 US quarts.
How many fluid ounces are in a liter?
33.81 US fluid ounces or 35.20 imperial fluid ounces. The imperial count is higher because its ounce is the smaller of the two.
Sources
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, Appendix B, National Institute of Standards and Technology.
- Weights and Measures Act 1985, Schedule 1 (definitions of units), legislation.gov.uk (The National Archives).
- SI Units - Volume, National Institute of Standards and Technology.