Volume converters

About volume conversions

Volume is where US customary and UK imperial units diverge the most dramatically of any measurement category — and where the divergence is most likely to catch someone off guard. A US fluid ounce (≈29.57 mL) is not the same size as an imperial fluid ounce (≈28.41 mL); a US liquid gallon (3.785411784 L) is roughly 20% smaller than a UK imperial gallon (4.54609 L); and even "a cup" means different things depending on whether a recipe was written in the US (≈236.6 mL customary, or exactly 240 mL on nutrition labels), Australia (250 mL metric cup), or a home cook eyeballing a mug.

These are not academic distinctions. Fuel economy figures quoted in "miles per gallon" mean different real-world efficiency depending on which gallon the source country uses — a US mpg figure and a historical UK mpg figure are not directly comparable without converting through the underlying gallon definition first, ideally to a shared unit like liters per 100 kilometers. Cooking sites frequently omit which cup, tablespoon, or fluid ounce they mean, which is one of the most common causes of a recipe not turning out as expected when adapted from a different country's food blog.

Medical and household dosing measurements add another layer: a "teaspoon" on a US medicine bottle is standardized to exactly 5 mL for dosing purposes, which is subtly different from a US customary teaspoon used in cooking (≈4.93 mL) — close enough that nobody worries about it in the kitchen, but precise dosing instructions use the rounded 5 mL figure specifically so a standard dosing spoon or syringe lines up correctly.

Volume conversions also intersect with weight in ways that trip people up: a cup of flour and a cup of water do not weigh the same, so converting a recipe from cups to milliliters preserves volume but not necessarily the intended proportion if the original recipe was really calibrated by weight. For precision baking, many cooks convert to grams by weight rather than relying on volume conversion at all — our volume converters are still useful for scaling liquid ingredients, understanding packaging sizes, and reading fuel or beverage container labels internationally.

Use these converters when scaling a recipe from another country, comparing fuel economy labels, converting a medical dosing instruction, or reading a beverage container's metric equivalent — and see our dedicated guide on the US gallon versus imperial gallon distinction if you are working with fuel, tank capacity, or historical UK measurements specifically.

Related reading: US gallon vs imperial gallon: what is the difference?