Liters to Imperial Gallons

Brewing a British Recipe on Kit That Is Marked in Litres

The recipe in the old brewing book is written for five gallons and the author never once says which gallon he means, because in Britain there was only one. Your boiler is graduated in litres, your fermenter has a 23 L line moulded into the side, and the malt on the bench is weighed in kilograms. One number has to move before the mash can be scaled.

Then there is the packaging end. Brewers still order casks by name rather than by volume, so a firkin, a kilderkin and a pin turn up in the same conversation as a 50 L keg. The names are all fractions of an imperial gallon count, which is why the litre figures come out uneven and worth writing down once.

Conversion factor: 1 L = 0.219969157 imp gal, and 1 imp gal = 4.54609 L exactly. The classic 23 L homebrew batch is therefore 5.06 imperial gallons — near enough to a five-gallon recipe that most kits are sold on the resemblance.

Why the Imperial Gallon Survives in British Brewing

Recipe books were never reissued in metric

A great deal of British brewing literature dates from before metrication and quotes grain in pounds against a gallon brew length. Reprints usually leave the original figures alone.

Cask names stand in for volumes

Nobody orders 81.83 litres, they order a kilderkin. Every one of those names is a multiple or fraction of the 36-gallon barrel, so the underlying unit is imperial even now.

Equipment arrives in round litres

Fermenters, boilers and modern kegs are made to metric sizes — 23 L, 30 L, 50 L — so the volume you can actually brew rarely lands on a whole number of gallons.

Duty and yield are worked in litres

UK alcohol duty is calculated from litres of pure alcohol in the finished product, so a commercial brewer keeps metric records even while talking to the trade in gallons.

Turning a Brew Length Into Cask Terms

Convert at two points in the process: when you scale the recipe before mash-in, and again on racking day when you find out what actually made it into the container.

Type the litre volume on the left

Use whatever your vessel is marked with. The decimal mark can be a comma or a dot and spaces are thrown away, so a figure pasted as 1 636 from a spreadsheet still reads correctly.

Read the gallon count immediately

There is no submit step; the second box moves with the keystrokes. Up to eight decimals are kept, which matters when you are checking whether a brew length really covers a nine-gallon cask.

Go the other way for an old recipe

Put the book's gallon figure into the right-hand box and the litre equivalent appears on the left, or press ↔ to swap the pair outright when the whole session is being scaled from imperial sources.

Drop the number into the brew sheet

Copy from either field to get the digits by themselves, without the unit or the space between thousands, which is what a brew log or a scaling spreadsheet expects. Ctrl + C in the field is equivalent.

Convert the packaged volume, not the kettle volume. What ends up in the cask is always less than what you boiled, so a batch scaled to exactly nine gallons will not fill a firkin. Work backwards from the container and add your usual losses on top.

The UK Cask Ladder From Pin to Hogshead

Every traditional cask below is defined as a whole number of imperial gallons, which is why the litre column is full of awkward decimals. Kegs came later and were built to metric sizes, so their gallon figures are the untidy ones instead.

Cask or keg	Imperial gallons	Litres	Imperial pints	Where it turns up
Pin	4.5 imp gal	20.46 L	36 pints	Beer festivals, small guest ales, home cask setups
Firkin	9 imp gal	40.91 L	72 pints	The standard cask
Kilderkin	18 imp gal	81.83 L	144 pints	Busy pubs and fast-moving house beers
Barrel	36 imp gal	163.66 L	288 pints	The base unit brewery output is counted in
Hogshead	54 imp gal	245.49 L	432 pints	Rare now, mostly maturation and special releases
Keg, 50 L	11.00 imp gal	50 L	88 pints	The common European keg for lager and craft
Keg, 30 L	6.60 imp gal	30 L	52.8 pints	Slower lines and smaller cellars
Cornelius keg	4.16 imp gal	18.93 L	33.3 pints	Homebrew dispense; it is a US five-gallon vessel

Notice how a 23 L batch sits: 5.06 imperial gallons is well short of a firkin, a shade over a pin, and slightly more than a Cornelius keg will take. That last mismatch is why a great many homebrewers rack into a corny and bottle the remainder.

Brewery output is counted in barrels. When a British brewery describes itself as a twenty-barrel plant it means the brew length of one batch, 20 × 163.66 L, or a little under 3300 litres into the fermenter.

What Helps on Brew Day and at Racking

Try several brew lengths in seconds

Because output follows every keystroke, you can test 21, 23 and 25 litres against a cask size without pressing anything between attempts.

Reads a gallon recipe backwards

Both boxes take input and the ↔ button reverses the pair, so an old book's gallon brew length becomes a litre target for your fermenter.

Numbers ready for the brew sheet

The copy button hands over the plain value with no unit and no thousands spacing, which pastes straight into a recipe spreadsheet or brewing software.

Pints, US gallons and millilitres too

The searchable dropdowns carry every volume unit the app knows, so the same page will take a batch to pints for a serving count or to US gallons for an American recipe.

Home Brewing and Cask Volume Questions

Why is a brewer's barrel 36 imperial gallons?

It is a survivor of the nineteenth-century tidy-up that replaced the older ale and beer gallons with the single imperial gallon, and the 36-gallon figure for beer stuck because everything else in the trade was defined against it. A kilderkin is half a barrel, a firkin a quarter, a pin an eighth and a hogshead one and a half. Wine and spirits casks and the 42-gallon oil barrel come from entirely separate trades and share nothing but the word.

What is the difference between a pin and a firkin?

Exactly a factor of two. A pin is 4.5 imperial gallons, or 20.46 litres, giving 36 pints; a firkin is 9 gallons, 40.91 litres and 72 pints. The firkin is the workhorse of the cask trade, while the pin exists for beers that will not sell fast enough to stay in condition — a cask has only a few days of life once it is broached, so putting a slow-moving speciality into a firkin usually means pouring half of it away.

How do I scale a recipe written in imperial gallons to litres?

Convert the brew length first, then scale every ingredient by the same ratio. Five imperial gallons is 22.73 litres; if your fermenter is filled to 23 litres the ratio is 23 ÷ 22.73 = 1.012, so a 4 kg grain bill becomes 4.05 kg and the hops rise by the same 1.2 per cent. Water treatment and hop bitterness scale with the volume too. Gravity does not scale — it is a concentration, so it stays whatever the original recipe targeted.

Why is a US five-gallon homebrew batch smaller than five gallons here?

Because the two countries kept different gallons. Five US gallons is 18.93 litres, whereas five imperial gallons is 22.73 litres — the imperial one is about 20 per cent larger. Brewing an American recipe straight into a 23 litre fermenter therefore stretches the batch by roughly a fifth, and the finished beer comes out noticeably thinner and less bitter than intended. Scale the whole ingredient list by 23 ÷ 18.93, or brew to 18.9 litres and accept the smaller batch.

Why does my packaged volume fall short of the batch size?

Beer is left behind at every transfer. Hot and cold break settle in the kettle, a heavy hop charge soaks up a litre or more on its own, yeast forms a cake in the fermenter, and dip tubes and hoses hold their own dead volume. Losses of five to ten per cent between kettle and container are ordinary, and a hoppy beer can lose more. If you want a firkin filled properly, aim the brew length a litre or two above nine gallons rather than exactly at it.