Firkin to Liter Converter

How it is calculated

The tool multiplies the number of firkins by two fixed factors. litres = firkins × 40.91481 and gallons = firkins × 9. The firkin is defined as 9 imperial gallons, and one imperial gallon is 4.54609 litres, which gives 9 × 4.54609 = 40.91481 L per firkin. Both results are rounded to two decimals and shown with L and gal. The gallon in the output is therefore the imperial (UK) gallon of about 4.546 L, not the US gallon of about 3.785 L. Decimals are accepted, so a half firkin is 0.5. Negative numbers are not rejected and just return negative volumes. A firkin is a unit of capacity for cask beer; actual casks vary a little, and a cask is rarely sold completely full of drinkable beer.

Common mistakes

• Treating the gallon result as a US gallon. 22.50 imperial gallons is about 27.0 US gallons, so the number would be far off for an American recipe or order.
• Mixing up the firkin with the keg or the barrel. A firkin is a quarter of a 36-gallon barrel (9 imperial gallons); a standard keg, a kilderkin and a pin are different sizes.
• Assuming that all of the cask can be served. Yeast sediment, venting and the beer left below the tap mean the usable volume is smaller than the cask size.
• Expecting other definitions of the firkin. This tool uses only the British 9-imperial-gallon cask; an old text that gives a different size for a firkin will not match.