Litres to Gallons Converter – US and Imperial, Side by Side

One liquid, two counts

The bars below follow the converter. Both describe exactly the same amount of liquid — the US bar runs longer only because US gallons are smaller, so it takes more of them.

The table people actually look up

Litres converted both ways at once — the amounts that come up for fuel tanks, fish tanks, water butts and brewing.

Goes with this conversion

The other converters people open alongside this one — weight, temperature, and the general-purpose box.

Litres to gallons in three steps

How the litres to gallons conversion works

Going deeper

Reference table: litres in both gallons

The converter above shows both gallon counts for any amount, but a reference table answers the question most people actually ask, which is what a familiar quantity, a fuel tank, a container, a recipe amount, looks like in the gallon system they are used to. The table below gives both counts for common litre amounts, computed from the two divisors on this page: a US gallon is 3.785411784 litres, and an Imperial gallon is 4.54609 litres. Gallon counts are shown to five decimal places, as on this page, because the difference between the two systems is itself only about twenty percent, and coarse rounding would hide it.

The 50-litre row is the fuel-tank row, and it shows why the gallon question matters at the pump: the same tank holds 13.21 US gallons but only 11.00 Imperial gallons, and a driver who converts a European tank capacity with the wrong divisor will misjudge the range by more than two gallons, or about nine litres of fuel. The 20-litre row is the container row: a standard jerry can holds 20 litres, which is 5.28 US gallons and 4.40 Imperial gallons, and the five-gallon cans sold on opposite sides of the Atlantic are not the same can at all, as the guide above explains for the five-gallon pair, which differ by nearly four litres. Whenever a capacity is quoted in gallons without saying which gallon, the table above is the check: divide by the wrong divisor and the answer is a fifth out, in the direction that flatters the seller if the gallon is Imperial and the buyer assumed US.

Why there are two gallons: a short history

There are two gallons because the gallon was standardised twice, in two countries, from two different definitions, and neither country then adopted the other’s. The United States gallon descends from the Queen Anne wine gallon of 1707, defined as 231 cubic inches, and the United States kept it after independence, so the US gallon today is still 231 cubic inches, which is 3.785411784 litres. The Imperial gallon was defined in Britain in 1824 as the volume of ten pounds of water at 62 °F, which is 277.42 cubic inches, or 4.54609 litres. Divide the Imperial definition by the US definition and you get 277.42 divided by 231, which is 1.20095, exactly the ratio the guide above derives from the litre definitions: an Imperial gallon is 1.20095 US gallons, or 20.095 percent bigger.

Britain itself has since moved on: petrol in the United Kingdom has been sold by the litre since metrication, and the Imperial gallon survives mainly in older fuel-economy figures, in the fuel consumption of older vehicles, and in the language of drivers who learned miles per gallon before litres per hundred kilometres. The United States never metricated fuel sales, so the US gallon remains the everyday unit there. Canada sits between the two systems, as the guide above notes: litres at the pump since metrication in the 1970s, but US-leaning gallons in print, advertising and older vehicle specifications, because the Canadian market shares vehicles, parts and publications with the United States. A Canadian driver reading a fuel-economy figure in gallons must therefore ask which gallon the publication means, because the same car will show a figure twenty percent higher in Imperial gallons than in US gallons, with no change in the car at all.

The fuel-economy trap: miles per gallon in two systems

Fuel economy is where the two gallons do their most expensive damage, because a miles-per-gallon figure without a gallon is a number without a unit, and the two possible units differ by a fifth. The conversion is simple once the ratio is known: miles per Imperial gallon equal miles per US gallon times 1.20095, because the Imperial gallon takes you further on the same amount of fuel only in the sense that it is a larger amount of fuel. A car rated at 30 miles per US gallon is rated at 36.03 miles per Imperial gallon, which is 30 times 1.20095, and a car rated at 40 miles per Imperial gallon manages only 33.31 miles per US gallon, which is 40 divided by 1.20095. Comparing a US figure with an Imperial figure directly, without converting, overstates the Imperial car’s economy by twenty percent, which is larger than the difference between many competing models.

Litres per hundred kilometres avoid the trap entirely, because they contain no gallon at all, and the conversion to them is worth knowing for the same reason. Litres per hundred kilometres equal 235.215 divided by miles per US gallon, because a hundred kilometres are 62.137 miles and a US gallon is 3.78541 litres, and 62.137 times 3.78541 is 235.215. The 30 miles per US gallon car therefore uses 7.84 litres per hundred kilometres, which is 235.215 divided by 30, and the same car at 36.03 miles per Imperial gallon gives the same 7.84 litres per hundred kilometres when the Imperial conversion is used, 282.48 divided by 36.03, where 282.48 is 62.137 times 4.54609. The two routes agree, as they must, because they describe the same physical consumption. When a fuel-economy comparison mixes systems, convert everything to litres per hundred kilometres first; it is the one figure that cannot be flattered by the choice of gallon.

Pints, fluid ounces and the smaller units

Below the gallon, the two systems diverge again, in the same direction and by the same ratio, and the smaller units are where cooking and container conversions most often go wrong. A US fluid ounce is one 128th of a US gallon, which is 29.5735 millilitres. An Imperial fluid ounce is one 160th of an Imperial gallon, which is 28.4131 millilitres. The US fluid ounce is therefore about four percent larger than the Imperial fluid ounce, even though the US gallon is twenty percent smaller than the Imperial gallon, because the two gallons are divided into different numbers of ounces. A recipe or a medicine measure that calls for fluid ounces without saying which system means a four percent difference in the amount, small for a drink and significant for a measured dose.

Pints follow the same pattern with a larger gap. A US pint is sixteen US fluid ounces, which is 473.18 millilitres, while an Imperial pint is twenty Imperial fluid ounces, which is 568.26 millilitres, a full twenty percent larger, tracking the gallon ratio. The converter above shows US pints and US fluid ounces for any amount entered, and the table in the first section gives the gallon counts from which the smaller units follow by multiplication: divide litres by 3.785411784 for US gallons, multiply US gallons by eight for US pints, and by 128 for US fluid ounces. For Imperial units, divide litres by 4.54609 for Imperial gallons, multiply by eight for Imperial pints, and by 160 for Imperial fluid ounces. The arithmetic is the same shape in both systems; only the divisors and the counts per gallon differ, and writing them down before converting is the cheapest insurance against a fifth-out error.

Aquariums, pools and tanks

Water volumes are where litre-to-gallon conversion is most often needed at domestic scale, because aquariums, hot tubs and swimming pools are sold, specified and dosed in different units depending on the manufacturer and the country. A home aquarium of 200 litres holds 52.83 US gallons, which is 200 divided by 3.785411784, and 43.99 Imperial gallons, which is 200 divided by 4.54609. The difference matters for dosing: a water treatment dosed per gallon at the US figure gives a different concentration than the same dose calculated at the Imperial figure, by twenty percent, which is enough to matter for sensitive fish and for chemical treatments with a narrow effective range. The safe practice is to dose from the litre figure the manufacturer prints on the treatment, or to convert the tank once, in the system the treatment uses, and to write that figure on the tank.

Swimming pools scale the same arithmetic up without changing it. A small pool of 50,000 litres holds 13,208.60 US gallons, which is 50,000 divided by 3.785411784, and 10,998.46 Imperial gallons, which is 50,000 divided by 4.54609. Pool chemicals, heaters and pumps are all specified against volume, and a heater rated for a pool in gallons will be undersized if the gallons are Imperial and the pool was measured in US gallons, or oversized in the reverse case, by the same twenty percent. The conversion itself is trivial; the error is always in the unstated system, which is why pool specifications should state litres alongside gallons, and why a pool owner converting a specification should do so from the litre figure wherever one is printed, rather than from a gallon figure of unknown system.

Barrels, drums and the oil barrel

Industrial containers carry their own gallon folklore, and the two commonest figures are both worth converting exactly. The oil barrel, the unit of the petroleum industry, is 42 US gallons, which is 42 times 3.785411784, giving 158.99 litres. It is not a physical barrel anyone ships oil in today; it is a unit of account that survives from the early Pennsylvania oil trade, when 42-gallon tierces were a standard container, and it persists because oil is priced per barrel and every market participant knows what a barrel means. A price quoted per barrel converts to a price per litre by dividing by 158.99, and a price per litre converts back by multiplying by the same figure, with no Imperial gallon anywhere in the calculation, because the oil barrel is defined in US gallons.

The steel drum is the physical container most people meet, and it carries a quiet trap. A standard drum is often called a 55-gallon drum, which is 55 times 3.785411784, giving 208.20 litres, while the metric drum sold alongside it is a 200-litre drum, which is 52.83 US gallons, as the aquarium section above shows. The two drums are not the same container: the 55-gallon drum holds 8.20 litres more than the 200-litre drum, a difference of about four percent, which matters when a drum is used as a measure for mixing, dosing or shipping, and which is invisible if both are described as a standard drum. When a specification calls for drums, check whether it means 55 US gallons or 200 litres, because the difference, though smaller than the US-to-Imperial gap, is large enough to break a formulation that depends on exact volumes.

Cooking volumes: cups, tablespoons and millilitres

Cooking is where litre conversion meets its messiest relatives, the cup and the spoon, because those units are defined differently in different countries and are often used as if they were universal. The United States customary cup is one sixteenth of a US gallon, which is 3,785.411784 divided by sixteen, giving 236.59 millilitres. The metric cup, used in Australia, New Zealand and much of modern recipe writing, is defined as 250 millilitres exactly, which is larger than the US cup by 13.41 millilitres, or about five and a half percent. A recipe that calls for four cups therefore calls for 946.35 millilitres in the US system and 1,000 millilitres in the metric system, a difference of more than fifty millilitres, which matters for baking, where liquid ratios are structural, and matters little for a soup, where they are not.

Spoons follow the same pattern at smaller scale. A United States tablespoon is one sixteenth of a US cup, which is 236.59 divided by sixteen, giving 14.79 millilitres, and a United States teaspoon is one third of a tablespoon, giving 4.93 millilitres. A metric tablespoon is commonly 20 millilitres in Australia, which is larger than the US tablespoon by more than a third, while a metric teaspoon is 5 millilitres, close enough to the US teaspoon to be interchangeable in most cooking. The practical rule is the same as for gallons: identify the system before converting, convert the system consistently through the whole recipe, and never mix a US cup with a metric tablespoon in the same dish, because the two systems’ ratios differ, and a recipe converted half in one system and half in the other is converted in neither. For liquids, this page’s litre conversions give the anchor: convert cups to millilitres first, then millilitres to gallons if a gallon figure is needed, rather than converting cups directly to gallons and compounding two system choices at once.

Fuel and water in everyday amounts

The amounts people actually convert are containers, not abstractions. A 20-litre jerrycan holds 5.28 US gallons or 4.40 Imperial gallons. A 50-litre car fuel tank holds 13.21 US gallons or 11.00 Imperial gallons — the Imperial figure lands almost exactly on a round number, which is a useful check: a 50-litre tank is, to three decimal places, 11 Imperial gallons. A 200-litre drum holds 52.83 US gallons or 43.99 Imperial gallons.

Water adds a second question: how much does a gallon weigh? Because a litre of water weighs one kilogram, the weight follows directly from the volume. One US gallon of water is 3.78541 kilograms, about 8.34 lb. One Imperial gallon of water is 4.54609 kilograms, about 10.02 lb — which is no coincidence, since the Imperial gallon was defined as the volume of ten pounds of water. Fuel weighs less than water, so a gallon of petrol weighs less than a gallon of water in either system; the volume conversion is exact, and the weight depends on the liquid.

Comparing fuel prices: price per litre vs price per gallon

Fuel prices are quoted per litre in most of the world and per gallon in the United States, and comparing them needs the same conversion as comparing volumes. A price of $3.50 per US gallon is $3.50 ÷ 3.78541 = $0.92 per litre. A price of £1.50 per litre is £1.50 × 4.54609 = £6.82 per Imperial gallon. The two figures describe the same fuel at very different prices, and the conversion is the only way to tell which is cheaper.

The same care applies to fuel economy. A car that returns 30 miles per US gallon uses 7.84 litres per 100 km, while a car that returns 30 miles per Imperial gallon uses 9.42 litres per 100 km — the same number, a different consumption, because the gallons differ. A miles-per-gallon figure without its gallon is meaningless, and a price-per-gallon figure without its gallon is worse, because it looks comparable when it is not. Convert both the volume and the price to the same unit before comparing, and the comparison is honest.

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