Volume Converter

Type a volume, pick the unit you have and the unit you want, and the result appears as you type. The list covers metric units from milliliters to cubic meters, the full US kitchen ladder from teaspoons to gallons, and the two imperial units that still trip people up: the UK pint and UK gallon. The output is the same physical quantity written a different way, so a larger number just means the target unit is smaller.

Where the liter comes from

The metric unit at the center of this converter is younger than the gallon it usually replaces. France introduced the liter in 1795 as one of the republican units of measurement, defining it as one cubic decimeter, a cube ten centimeters on a side. The name traces back through the older French litron to the Byzantine Greek litra, which was a unit of weight rather than volume. The early metric system deliberately tied volume to mass: the gram was set as the mass of one cubic centimeter of water at the melting point of ice, so a liter of water weighed almost exactly one kilogram. That near-coincidence proved too useful to leave alone.

In 1901 the third General Conference on Weights and Measures made the link official, redefining the liter as the volume occupied by one kilogram of pure water at its temperature of maximum density, about 3.98°C, under one atmosphere. The trouble was that the physical kilogram prototype turned out to be roughly 28 parts per million too large, so this water-based liter came out to about 1.000028 cubic decimeters, slightly bigger than the tidy cube it was meant to be. For six decades "liter" and "cubic decimeter" were not quite the same thing. The twelfth conference tidied this up in 1964, returning the liter to its original definition of exactly one cubic decimeter. That is the value this converter uses, which is why one milliliter equals exactly one cubic centimeter and one cubic meter equals exactly 1000 liters.

How the gallon split in two

The English-speaking world never had a single gallon. By the eighteenth century at least three were in daily use: the corn or Winchester gallon of about 268.8 cubic inches for grain, the ale gallon of 282 cubic inches for beer, and the wine gallon of 231 cubic inches for wine and spirits. A statute of Queen Anne passed in 1706 and in force from 1707 fixed the wine gallon at exactly 231 cubic inches, the volume of a cylinder seven inches in diameter and six inches deep when pi is taken as the old workshop approximation 22/7.

Britain swept this tangle away in 1824. The Weights and Measures Act abolished every existing gallon and replaced them with a single imperial gallon, defined as the volume of ten pounds of distilled water weighed in air at 62°F under a barometric pressure of 30 inches of mercury, which came to about 277 cubic inches. The United States, independent for nearly fifty years, did not follow. It kept the old 231-cubic-inch wine gallon: on the recommendation of Ferdinand Rudolph Hassler the Treasury adopted that gallon as the national standard in 1832, and a joint resolution of Congress on 14 June 1836 approved the choice and ordered matching standards made for the customhouses. From that single decision flow all the differences between US and imperial volume that this tool has to keep apart: the pint, the quart, the gallon and the fluid ounce all inherit the split.

Both gallons are now defined against the meter rather than against water, but they arrived there separately and late. Britain's Weights and Measures Act 1963 still described the imperial gallon in terms of ten pounds of distilled water of a stated density weighed in air, a mouthful that worked out to 4.546092 liters. The rounder figure of exactly 4.54609 liters was taken up in Canada first and adopted in the United Kingdom in 1976; it is the value written into the UK Weights and Measures Act 1985, which in the same schedule fixes the imperial pint at 0.56826125 cubic decimeters. The US gallon, at 231 cubic inches, became exactly 3.785411784 liters once the International Yard and Pound Agreement of 1959 set the inch at 25.4 millimeters, a change that took effect on 1 July that year.

How the conversion works

Each unit is stored as an exact factor in liters, so every conversion is a single multiply and divide:

result = value × liters_from ÷ liters_to

The defaults convert 2 liters to US gallons: 2 ÷ 3.785411784 = 0.5283 gal. None of the factors are approximations. The US gallon has been exactly 3.785411784 liters since the inch was fixed at 25.4 mm in 1959, and the imperial gallon has been exactly 4.54609 liters since Britain adopted that value in 1976. Because every unit shares the same reference point, the direction never introduces rounding: convert gallons to liters and back and you land on the number you started with.

The pint and gallon trap

The US and UK share unit names but not unit sizes. A US pint is 16 US fluid ounces, about 473 ml; a UK pint is 20 imperial fluid ounces, about 568 ml. The gallons inherit the same 20% gap. This matters beyond the pub: a car rated at 40 mpg on UK figures manages only about 33.3 mpg measured in US gallons, which makes British and American fuel-economy numbers look further apart than the cars actually are. Canadian pumps switched from imperial gallons to liters in 1979, and older Canadian mileage figures use the imperial gallon, not the US one.

Fluid ounces and why the counts differ

The fluid ounce carries the 1824 split down into the smallest everyday unit. Britain divided its imperial gallon into 160 fluid ounces, making each imperial fluid ounce 28.413 ml, close to the volume of one avoirdupois ounce of water, which is where the name comes from. The US divided its smaller wine gallon into 128 fluid ounces, so a US fluid ounce is 29.574 ml, about 4% larger. The counterintuitive result is that a liter holds more of the smaller imperial ounces, 35.195, than of the larger US ounces, 33.814. Only the US figure reaches packaging, which is why a 500 ml bottle is labeled 16.9 fl oz in an American store.

Cups and spoons are not universal

This converter uses the US customary cup of 236.588 ml, because that is what American recipes mean. Australian and New Zealand recipes use the 250 ml metric cup, and US nutrition labels use a rounded legal cup of exactly 240 ml. Spoons vary too: Australia defines the tablespoon as 20 ml, one teaspoon more than everyone else's 15 ml. In a sauce nobody will notice. In a cake batter with 3 tablespoons of baking powder, the extra 15 ml can.

What this converter does not do

Volume is not weight. A cup of water is 237 g, but a cup of flour is roughly 120 g and a cup of honey about 340 g, so converting a recipe between cups and grams needs a density table — that is what the cups-to-grams converter is for. Also missing on purpose: the US dry pint of 550.6 ml used for berries and produce, which is a different unit from the liquid pint despite the shared name.

Frequently asked questions

How many liters are in a gallon?

Depends on the gallon. A US gallon is exactly 3.785411784 liters, while a UK (imperial) gallon is exactly 4.54609 liters — about 20% larger. If a recipe or fuel figure just says gallons, check which country it comes from before converting.

Why is a UK pint bigger than a US pint?

The two systems split in 1824, when Britain redefined its gallon as the volume of 10 pounds of water and the US kept the older wine gallon of 231 cubic inches. A UK pint is 20 imperial fluid ounces, about 568 ml, while a US pint is 16 US fluid ounces, about 473 ml. A pint of beer in London really is a fifth larger than one in New York.

How many ml are in a cup?

A US customary cup, the one this converter uses, is 236.588 ml. The metric cup used in Australian and New Zealand recipes is 250 ml, and US nutrition labels round the cup to a legal 240 ml. For most cooking the 5% spread does not matter, but in baking it can.

Is a tablespoon 15 ml or 20 ml?

In the US, UK, Canada and New Zealand a tablespoon is 15 ml for practical purposes — the exact US definition is 14.79 ml. Australia is the outlier with a 20 ml tablespoon equal to 4 teaspoons. An Australian recipe calling for 2 tablespoons means 40 ml, a third more than the 29.6 ml a US cook would measure.

How many fluid ounces are in a liter?

One liter is 33.814 US fluid ounces, which is why a 500 ml bottle is labeled 16.9 fl oz in the US. The imperial fluid ounce is slightly smaller in volume terms per liter count — a liter is 35.195 imperial fluid ounces — but only the US measure appears on modern packaging.