Barrels — one word, six different volumes
'One barrel' has meant different things to different industries for 400 years. Here is the six-variant lookup table.
The barrel was originally the volume of a physical cask, and different trades built casks in different sizes. Every industry that survived past the Industrial Revolution kept its own barrel — legally defined but not standardised across trades.
The variants
Oil barrel (bbl) = 42 US gal = 158.987 L > US liquid barrel = 31.5 US gal = 119.24 L > US beer barrel = 31 US gal = 117.35 L > UK beer barrel = 36 UK gal = 163.66 L = 43.23 US gal > Dry barrel = 26.25 US gal = 115.63 L (US) > Cranberry barrel = 5,826 in³ = 95.47 L (US, still legal)
Where each shows up
Oil markets: exclusively the 42-gallon bbl. WTI and Brent futures are priced per bbl. Brewing: US commercial keg sizes are fractions of the 31-gal beer barrel (a 'half barrel' keg is 15.5 gal). UK CAMRA data on pub cellars uses the 36 UK-gal beer barrel. Grocery statistics still occasionally cite dry barrels for fruit and vegetables.
Why oil is 42 gallons
The Pennsylvania Petroleum Producers Association adopted the 42-gallon standard in 1866, matching the tierce — a wine cask used to ship whale oil. It was chosen because a 42-gal wooden cask could be handled by one man; a 45-gal cask could not. The size stuck when steel drums replaced wood and the industry globalised.
Worked example — a 1,000-barrel oil order
1,000 bbl × 158.987 L = 158,987 L = 158.99 m³. At 850 kg/m³ for medium crude, that is 135.14 tonnes. A road tanker holds 30–40 m³, so a 1,000-bbl order is 4–5 truckloads. A rail tank car holds 100–120 m³ — about 700 bbl per car.
The five-second recap
Oil bbl = 42 gal = 159 L. US beer barrel = 31 gal = 117 L. UK beer barrel = 36 UK gal = 164 L. Always specify which barrel.
Try the converters mentioned in this article
FAQ
How much does an oil barrel weigh?+
The oil weighs 130–140 kg depending on API gravity. The steel drum itself adds about 22 kg.
How many pints in a US beer barrel?+
31 gal × 8 pints = 248 US pints. In the UK, 36 UK gal × 8 = 288 UK pints.
Do oil companies actually ship in barrels?+
No — pipelines and supertankers dominate. The barrel is now a pricing and accounting unit, not a physical container.
This article was written by The Turbo Unit Converter engineering desk (Industrial metrology) and last reviewed on 2026-06-28 against NIST SP 811 and the BIPM SI Brochure. Read our full editorial policy.