Volume & Capacity

Volume measures the three-dimensional space occupied by a substance. In cooking and food, volume units dominate — cups, tablespoons, and millilitres. In science and medicine, the millilitre (equal to one cubic centimetre) is standard. In fuel and large containers, litres and gallons are used. The most persistent source of confusion is the difference between the US gallon (3.785 L) and the UK imperial gallon (4.546 L), and between the US fluid ounce and the UK fluid ounce — the same names but different volumes.

Units

Litres (L): One cubic decimetre — the volume of a cube with sides of exactly 10 cm. The standard unit for liquids in metric countries. Scale: A standard 1-litre water bottle. Example: A large pot of soup might hold 4 litres.
Millilitres (mL): One thousandth of a litre, equal to one cubic centimetre (cm³). Used in medicine, cooking, and laboratory measurement. Scale: A standard teaspoon holds about 5 mL. Example: A typical shot of espresso is 30 mL.
US Gallons (US gal): Exactly 231 cubic inches = 3.785 411 784 litres. The standard liquid gallon in the United States. Scale: About the volume of a large jug of milk. Example: A standard US fuel pump dispenses in US gallons.
Cups (c): Exactly 236.588 mL (one half of a US pint). The standard cooking measure in US recipes. Scale: About the volume of a large coffee mug. Example: Most US baking recipes measure flour in cups.
US Fluid Ounces (fl oz): One eighth of a US cup — exactly 29.573 5 mL. Note: the UK fluid ounce is 28.413 mL. Scale: About two tablespoons. Example: A standard US shot glass holds 1.5 fl oz.
Tablespoons (tbsp): One sixteenth of a US cup — exactly 14.787 mL. Used for small quantities in cooking. Scale: About three times the volume of a teaspoon. Example: Most recipes call for 1–4 tablespoons of oil.

Key Facts

The US gallon and UK imperial gallon differ by about 20% — a fact that regularly confuses fuel economy comparisons between US and UK cars.
One millilitre of water weighs exactly one gram at 4°C — a convenient fact that links volume and mass in the metric system.
The Australian metric cup is 250 mL; the US cup is 236.6 mL — close enough that most recipes are unaffected, but precise baking can differ.
A US fluid ounce (29.57 mL) differs from a UK fluid ounce (28.41 mL) despite sharing the same name.
Wine bottles are standardised at 750 mL by international agreement — exactly 25.36 US fl oz.

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