Volume Converter Guide: Liters, Gallons, Cups, and Milliliters

Volume is the unit family with the most traps, because two countries use the same words for different amounts. A US gallon is not an imperial gallon, a US pint is not a UK pint, and an Australian tablespoon is larger than everyone else. Knowing which system a recipe or spec sheet came from matters as much as the arithmetic.

The Metric Side Is Simple

One litre is 1,000 millilitres, and one millilitre equals one cubic centimetre exactly. A cubic metre is 1,000 litres. Because water has a density near 1 g per ml, 500 ml of water weighs about 500 g, which is why metric cooks can weigh liquids instead of measuring them. That equivalence does not hold for oil at roughly 0.92 g per ml or honey at about 1.42.

US Versus Imperial

• 1 US gallon = 3.785 litres; 1 imperial gallon = 4.546 litres
• 1 US fluid ounce = 29.57 ml; 1 imperial fluid ounce = 28.41 ml
• 1 US pint = 473 ml (16 fl oz); 1 imperial pint = 568 ml (20 fl oz)
• 1 US quart = 946 ml; 1 imperial quart = 1,137 ml

The gallon difference is 20%, which is why fuel economy figures look so different between markets: 30 miles per US gallon is 36 miles per imperial gallon, the same car and the same fuel.

Cooking Measures That Vary

The Australian tablespoon catches people out on baking recipes, where four tablespoons of butter can end up 20 ml over. When a recipe matters, weigh the ingredient in grams instead; it removes the whole problem.

Dry Cups Are Not Liquid Cups

A cup measures volume, but flour compresses. Scooping a cup straight from the bag can pack in 150 g of flour while spooning and levelling gives about 120 g, a 25% difference that shows up as dry, dense cake. Baking recipes that give grams are being helpful rather than fussy. For reference, a US cup holds roughly 120 g of plain flour, 200 g of granulated sugar, 220 g of butter, and 340 g of honey.

Volume From Dimensions

A rectangular container is length times width times height. A tank 80 cm by 40 cm by 50 cm holds 160,000 cubic centimetres, which is 160 litres. A cylinder is pi times radius squared times height, so a barrel of 30 cm radius and 90 cm height holds pi x 900 x 90 = 254,469 cubic cm, about 254 litres. A sphere is four thirds pi r cubed. These come up constantly for aquariums, water butts, and planters, and the cubic centimetre to litre step is just dividing by 1,000.

Cubic Units and the Cubing Trap

Linear conversions do not carry across to volume unchanged. There are 2.54 cm in an inch, but 16.387 cubic cm in a cubic inch, because the factor is cubed. Likewise a cubic metre is not 100 but 1,000,000 cubic centimetres, and a cubic foot is 28.32 litres. Forgetting to cube is the single largest source of order-of-magnitude errors in volume work, and it is worth checking any surprising answer against this rule.

Everyday Reference Volumes

• Standard wine bottle: 750 ml, which is 25.4 US fl oz
• Soft drink can: 330 ml in Europe, 355 ml in the US
• Car fuel tank: 45 to 60 litres, or 12 to 16 US gallons
• Bathtub filled for a bath: roughly 80 to 120 litres
• Domestic kettle: 1.5 to 1.7 litres

Fuel Economy Both Ways

Litres per 100 km and miles per gallon are reciprocal measures, so converting needs a division rather than a multiplication. For US mpg, divide 235.2 by the litres per 100 km figure: 7 l/100 km is 33.6 mpg. For imperial mpg, divide 282.5 instead, giving 40.4 mpg for the same car. Lower is better in one system and higher is better in the other, which is worth remembering before comparing two brochures.

Measuring Accurately

Read a liquid measure at eye level and use the bottom of the meniscus, the curved surface, as the line. Fill jugs on a flat surface rather than holding them, since a tilt of a few degrees changes the reading noticeably in a wide jug. For small amounts under about 15 ml, spoons are more accurate than the lowest marks on a large jug.

Convert Volumes Free

Our volume converter on SimpleCounter handles millilitres, litres, cubic centimetres and metres, US and imperial fluid ounces, pints, quarts, gallons, cups, tablespoons, and teaspoons, with the US and imperial variants kept separate so you cannot mix them by accident. It is free and runs entirely in your browser.