Volume unit conversion
US and UK gallons are not the same size — check which system your recipe, bottle label or fuel receipt actually uses before converting.
Unit converter
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| From | To | Multiply by |
|---|---|---|
| 1 liter (L) | milliliters (mL) | 1000 |
| 1 liter (L) | cubic meters (m³) | 0.001 |
| 1 cubic meter (m³) | liters (L) | 1000 |
| 1 US gallon | liters (L) | 3.78541 |
| 1 UK gallon | liters (L) | 4.54609 |
| 1 US gallon | US quarts | 4 |
| 1 US quart | US pints | 2 |
| 1 US pint | US cups | 2 |
| 1 US cup | US fl oz | 8 |
| 1 US fl oz | milliliters (mL) | 29.5735 |
| 1 UK fl oz | milliliters (mL) | 28.4131 |
| 1 tablespoon (US) | milliliters (mL) | 14.7868 |
| 1 teaspoon (US) | milliliters (mL) | 4.92892 |
Notes
- Cooking “cup” sizes also vary by country; see the cooking sheet for kitchen focus.
- Fuel economy often mixes L/100 km and MPG — see fuel-economy-conversion.
How the math works
Volume measures three-dimensional space, so it scales as length cubed. The metric ladder is built on powers of ten: the liter is defined as exactly one cubic decimeter, which means 1 m³ = 1000 L and 1 L = 1000 mL by definition, with no rounding involved. Every step between cubic units multiplies by 1000: 1 m³ = 1000 L = 1,000,000 mL. Conversions are pure multiplication because volume scales have a true zero — zero liters means no volume — so ratios behave consistently at any size. The US customary chain works the same way: 1 gallon = 4 quarts = 8 pints = 16 cups = 128 fluid ounces, matching the 4, 2, 2 and 8 factors in the table, and anchored to the metric system by 1 US gallon = 3.78541 L.
Common mistakes to avoid
The biggest trap is that US and UK units share names but not sizes. A UK gallon is 4.54609 L — about 20% more than the US gallon's 3.78541 L — yet the UK fluid ounce, 28.4131 mL, is smaller than the US fluid ounce, 29.5735 mL. That reversal surprises many people. Next, don't treat a US cup (8 fl oz ≈ 236.6 mL) as a 250 mL metric cup; across a four-cup recipe that drift exceeds 50 mL. Tablespoon and teaspoon values are ambiguous too: the exact US values are 14.7868 mL and 4.92892 mL, while the common kitchen convention is 15 mL and 5 mL. Finally, remember to divide when converting in the other direction — the most frequent arithmetic error in this kind of table.
Practical reference points
In the kitchen, memorize three anchors: 1 US cup ≈ 237 mL, 1 US tablespoon ≈ 14.8 mL and 1 US teaspoon ≈ 4.9 mL, so a recipe calling for 2 cups of milk needs about 473 mL. For beverages, note that a US pint is 16 fl oz while a UK pint is 20 fl oz — one reason a British beer looks bigger. Fuel economy works the same way: mpg figures from the US and UK are not comparable because the gallons differ, UK mpg reading roughly 20% higher for the same consumption. Engine sizes are quoted in liters worldwide (a "2.0-liter" engine), which makes the liter the natural bridge between cooking, automotive and beverage measurements.
Regional and standard differences
The liter is standard nearly everywhere and is accepted for use with the SI, so metric units dominate globally. The United States uses US customary units, and the United Kingdom retains imperial pints for beer and milk, which is why both countries still need explicit US/UK labels. In the US, the fluid ounce is fixed at 29.5735 mL exactly for nutrition labels. Watch the tablespoon especially: Australia and New Zealand use a metric tablespoon of 20 mL, versus the US 14.79 mL — a 35% difference that matters in baking. Before following any recipe or specification, check which standard it declares, and use the table above to convert within the matching system.
Frequently asked questions
- How many liters are in a US gallon?
- One US gallon equals 3.78541 liters. The UK (imperial) gallon is larger, at 4.54609 liters.
- How many milliliters are in a cup?
- A US cup is 8 US fluid ounces, about 236.6 mL. Other countries define the cup differently, so check your recipe's origin.
- Is a US fluid ounce the same as a UK fluid ounce?
- No. A US fluid ounce is about 29.57 mL, while a UK fluid ounce is about 28.41 mL.