Volume Converter

How to Convert a Volume

Features

A Cup Is Not a Cup

An American recipe calls for "1 cup of flour." A British or Australian baker, working from the metric cup their own recipes use, reaches for 250 mL. The US customary cup is actually 236.5882365 mL — a 5.6% difference that sounds small until it is the reason a cake comes out dense or a batch of bread dough is too wet. It gets messier with spoons: a UK or international tablespoon is 15 mL, an Australian one is 20 mL, and the US tablespoon lands at 14.79 mL — three different amounts all called by the same word, in the same language, sometimes on the same website, and a genuine 35% swing between the smallest and largest of the three. None of this is carelessness; it is what happens when three different countries standardised their kitchens a century apart without comparing notes. There is even a third cup lurking in older British cookbooks — a historic Imperial cup of 284.13 mL, tied to the old UK pint rather than the metric system at all — though it has mostly fallen out of use since the UK went metric for cooking measures, surviving mainly in the odd vintage cookbook still sitting on a shelf.

The Two Gallons

The gap gets wider outside the kitchen. A US gallon is 3.785411784 L. A UK (Imperial) gallon is 4.54609 L — almost 20% bigger, not a rounding difference. The split dates to 1824, when Britain redefined its gallon as the volume of exactly ten pounds of water, discarding several older, inconsistent gallons in one legal stroke. The newly independent United States never adopted that reform and kept using an older English wine gallon from 1707 instead — the two have been drifting apart on paper ever since, even though neither country's definition has changed since. The practical result shows up on fuel economy stickers: a car rated at 30 mpg in the US and one rated at 30 mpg in the UK are not equally efficient — the UK figure is measured against the bigger gallon, so it represents meaningfully better real-world fuel economy for the same number on the sticker. A "20-gallon" fuel tank tells the same story: a US spec sheet means 75.7 litres, while a UK spec sheet for the identically worded tank means 90.9 litres — a 15-litre gap hiding behind one unchanged word. The litre itself sidesteps all of this by definition — exactly 1,000 cubic centimetres, and exactly one-thousandth of a cubic metre — which is precisely why it, rather than either gallon, ended up as the base unit this entire converter is built on.

A Cake, a Fuel Tank, and a Dose

A home baker following a British blog wants to know what "125 mL of milk" means on a US measuring cup — the answer, about 0.53 cup, goes straight into the recipe without a second google search. A traveller renting a car in London sees a 55-litre tank and wants to compare it against the 14-gallon tank on their car back home in the US — converted, that US tank holds 53 litres, close enough that the rental car's slightly larger tank barely changes the maths on a fill-up budget. And a parent measuring a child's liquid medicine reads a dose in millilitres off a syringe but the box states it in teaspoons — getting that conversion exactly right, not approximately right, is the kind of case this tool was built to never fumble, converting 5 mL to almost exactly 1 US teaspoon rather than rounding it away. Further from the kitchen, an HVAC contractor sizing a room's airflow moves between cubic feet and cubic metres constantly, since ductwork specs and international equipment ratings rarely agree on which one to use.

Two Numbers for Every Fraction

Rather than pick a side in the US-vs-metric cup argument, the Recipe Fractions panel below the main converter shows both for every common baking fraction — 1/3 cup, 2/3 cup, 3/4 cup, and the rest — so a recipe from either tradition can be read at a glance without guessing which standard it was written against. The same Precision control used everywhere else on this page applies here too: Auto keeps everyday numbers short, while a fixed decimal setting is there for anyone converting a formulation or lab dilution rather than a dinner recipe. Above the all-units table, three filter chips — Metric, US Customary, UK & Imperial — narrow nineteen units down to just the family that matters for whatever is actually being converted. Nineteen is a deliberately wide net: alongside the everyday litre, cup, and gallon sit centilitres for European wine labels, cubic inches for engine displacement, and both the UK Imperial fluid ounce and its US counterpart side by side, so a single tool covers the kitchen, the fuel pump, and the machine shop without sending anyone hunting for a second converter.

Bottles, Barrels, and Standard Sizes

Some volume figures aren't really conversions at all — they're fixed names attached to a specific number, and it helps to know them going in. A standard wine bottle is 750 mL, a figure that settled into place partly because it was a convenient size for a glassblower's lungs and partly because it matched an old imperial gallon splitting neatly into six bottles. A magnum is exactly two standard bottles (1.5 L), a jeroboam is four (3 L), and the names keep escalating — through rehoboam, methuselah, and salmanazar — for large-format bottles mostly seen at auctions and weddings rather than supermarket shelves. Beer complicates things further: a UK pub pint (568.26 mL) is poured to a different legal standard than a US pint (473.18 mL) served across the same bar menu on an American franchise site, and a keg is typically sized in either UK or US gallons depending on where it was filled, which is exactly the kind of gap this converter's US-vs-UK unit split was built to close. None of these named sizes need their own entry in the unit list above — a magnum is just 1.5 L and a UK pint is just 568.26125 mL, so once the base units are covered, every named bottle or cask size is one multiplication away rather than a separate lookup.

What's Not in the Recipe

This converter moves between volume units only — it does not know the density of flour, honey, or anything else, so it cannot tell you how many grams are in a cup of a specific ingredient; that conversion depends on what is being measured, not just how much space it takes up, and belongs on the Cooking Measurement Converter or the Weight Converter instead. Nothing typed here leaves the browser tab — the arithmetic runs as plain JavaScript with no server call and nothing logged, which matters for a confidential formulation or an unpublished recipe. And for anything with medical or regulatory weight behind it — a dosage, a fuel-economy claim, a commercial batch size — treat the result as a fast, accurate conversion of a figure you already trust, not a substitute for the original measurement, and the tool keeps working identically with no internet connection at all once the page has loaded.