Volume Converter

US vs. Imperial: Two Different Systems

The most important thing to know about volume conversion is that US customary units and Imperial (UK) units share the same names but have different sizes. A US gallon is 3.785 liters; a UK (Imperial) gallon is 4.546 liters — about 20% larger. A US pint is 473 ml; a UK pint is 568 ml. A US fluid ounce is 29.57 ml; a UK fluid ounce is 28.41 ml. Whenever a recipe, fuel spec, or product label says "gallon" or "pint," confirm whether it means US or UK before converting.

Key Conversion Factors

• 1 US gallon = 3.78541 liters = 4 quarts = 8 pints = 128 fl oz
• 1 UK gallon = 4.54609 liters
• 1 liter = 0.264172 US gallons = 33.814 US fl oz
• 1 US cup = 236.588 ml (8 US fl oz)
• 1 tablespoon = 14.787 ml (3 teaspoons)
• 1 teaspoon = 4.929 ml

Practical example: a European recipe calls for 500 ml of milk. In US cups that is 500 ÷ 236.588 ≈ 2.11 cups, or just over 2 cups and 1.5 tablespoons.

Cooking, Fuel, and Industrial Uses

In cooking, volume measurements are used for liquids and loosely for dry ingredients like flour and sugar (though weighing dry ingredients is more accurate). US recipes use cups, tablespoons, and teaspoons almost exclusively. Most other cuisines use milliliters and grams. The FDA requires US nutrition labels to list serving sizes in both household units and metric for liquid foods.

For fuel economy, the US quotes miles per gallon (mpg) using US gallons. UK mpg uses Imperial gallons, so UK fuel economy figures appear about 20% better than US ones for the same vehicle. Canada and most other countries use liters per 100 km (L/100 km), where lower is better — the inverse of mpg.

Industrial and scientific contexts use liters and cubic meters (1 m³ = 1,000 liters) or cubic centimeters (1 cm³ = 1 ml) throughout.