Convert barrels to litres

An oil barrel holds 42 US gallons, which is exactly 158.987294928 litres. The US gallon is defined as 231 cubic inches, or exactly 3.785411784 litres, so the barrel has an exact value in litres too[1]. The formula is litres = barrels × 158.987.

Beer is measured in barrels as well, and the numbers change. US federal rules define the beer barrel as 31 gallons, which is 117.35 litres[2]. The British beer barrel holds 36 imperial gallons, or 163.66 litres[3]. You pick each of them with the Barrel type switch, and the line under it reminds you how many gallons each one holds.

You may also come across 119.24 litres. That is the 31½-gallon barrel that many US state laws fix as the barrel for liquids[1]. Neither oil nor beer is traded in it, but some converters use it for a plain barrel, so the switch has it as US liquids.

If you are more at home with US units, a litre is a little more than a quart: 1.057 US quarts, as the quarts to litres converter shows. The reverse calculation runs in the litres to barrels converter. The same barrels in US or imperial gallons are in the barrels to gallons converter.

A barrel is a unit of volume from the US customary system, written bbl. It is not part of the SI, yet crude prices on world exchanges are quoted in US dollars per barrel. It is built from gallons, so every barrel can also be written in gallons, and those you can turn into litres with the gallons to litres converter. On the other side stands the litre, the metric unit equal to one cubic decimetre.

The number 42 goes back to the first oil wells. The US petroleum industry was born in Pennsylvania in 1859, and oil was poured into casks of every size, so buyers never knew how much oil they were getting for their money. In August 1866 producers in Titusville agreed that a barrel of oil would hold 42 gallons[4]. That was the size of the tierce, a cask long used to ship herring, salmon, molasses and whale oil. Filled with crude, it weighed more than 300 pounds, about as much as one man could wrestle[4].

In 1872 the Petroleum Producers Association of the Pennsylvania oil region adopted the standard[4]. Today oil moves by pipeline and tanker, and the barrel stayed on as the unit in which exchanges quote prices and many oil companies report output.

A full US beer barrel is 117.35 litres, but bars get their beer in kegs that are fractions of it. Federal rules allow kegs of a whole barrel, a half, a third, a quarter, a sixth and an eighth[6]. The keg you see most often is the half barrel of 15.5 gallons, or 58.67 litres[7]. A quarter barrel holds 29.34 litres and a sixth barrel 19.56 litres.

In the UK, cask ale usually arrives at the pub in a firkin, a quarter of a beer barrel: 9 imperial gallons, or 40.91 litres[3]. The Campaign for Real Ale plans beer festivals in kilderkins, which hold two firkins, so 81.83 litres[3]. Across Europe the most common keg holds 50 litres, and the UK uses a keg of 11 imperial gallons, which comes to 50.007 litres[7].

Wine barrels are containers rather than units, so their size is set by tradition in each region. The common Bordeaux barrel holds 225 litres and the Burgundy barrel 228 litres[8].