Cask ale sizes: firkin, pin, kilderkin explained

Last updated: 29 June 2026

Most pub licensees can’t tell you the difference between a firkin and a kilderkin without checking the brewery invoice — yet the size of the cask you’re pulling from directly affects your cost per pint and your weekly stock variance.

I spent years losing track of partial kegs, mixing up container sizes, and accepting huge variances between what my till said sold and what my cellar count showed. The real problem wasn’t theft or over-pouring — it was that I didn’t actually know the capacity of half the casks sitting in my cellar.

This matters because a 1% loss on wet sales quietly costs a typical pub £3,000–£5,000 a year, and most of that loss comes from measurement error and forgotten partial stock, not deliberate waste. Once I learned to dip every cask, weigh open bottles, and reconcile the actual measures against till data the same day, my weekly variance went from guesswork to a number I could trust within a fortnight.

In this guide, I’ll walk you through every cask size you’ll encounter on draught, how to measure them properly, and how to build a stock routine that actually catches losses before they become profit leaks.

Let’s be clear: you don’t need fancy equipment or complicated spreadsheets. You need to know what you’ve got, how much is in it, and whether it matches what the till says went out.

UK cask ale sizes and volumes explained

The standard UK cask sizes are: barrel (163.6 litres), kilderkin (81.8 litres), firkin (40.9 litres), and pin (20.4 litres). Every size is exactly half the one above it, which makes the maths simple once you remember the hierarchy.

In practice, you’ll almost never see a barrel or kilderkin in a typical pub cellar. Most draught ale comes in firkins or pins. Lagers, stouts, and keg beers sometimes come in larger formats, but if you’re buying cask ale from your brewery, it’s a firkin or pin about 95% of the time.

Barrel (hogshead)

163.6 litres (36 imperial gallons). This is the largest standard cask. Breweries use these for bulk orders, festivals, and high-volume accounts. You won’t see one in your cellar unless you’re running a high-turnover flagship pub or a beer festival.

Kilderkin

81.8 litres (18 imperial gallons). Half a barrel. Some regional breweries offer kilderkins for pubs that want something between a firkin and a barrel. I’ve seen maybe three in my 15 years. It’s a format that exists more in theory than in practice.

Firkin (the workhorse)

40.9 litres (9 imperial gallons). This is the most common cask ale size in the UK. A firkin will give you roughly 73–80 pints depending on head loss and pour consistency. It’s small enough to handle, large enough to minimise turnover, and standard enough that every brewery stocks it. If you’re buying cask ale and don’t specify a size, it will arrive as a firkin.

Pin

20.4 litres (4.5 imperial gallons). Half a firkin. Some pubs use pins for seasonal brews, trial kegs, or lower-turnover ales. Pins are less common than firkins but you’ll see them regularly enough.

There’s also the ninth (a quarter firkin, 10.2 litres), but it’s rare in modern pubs and most breweries don’t stock them as standard. I’ve never ordered one deliberately.

How to measure cask ale stock accurately

Here’s where most pubs fail: they assume a cask is full when it arrives, and they never check it again until it’s empty. That’s where losses hide.

Measure every cask you put on with a calibrated dipstick, on the day it arrives, before you connect it to your font. You need to know the starting level so you can reconcile what came out against what the till recorded.

The dipstick method

A dipstick is a long, thin ruler marked in litres and pints. It costs £8–£15, and it’s the only way to measure cask stock accurately without guesswork. You lower it into the cask bung hole until it touches the bottom, withdraw it, and read the level. The number you get is the depth of liquid in the cask, which you then cross-reference against a conversion table (every brewery supplies these) to get the actual volume.

Most dipsticks come with conversion tables printed on the back. If yours didn’t, ask your brewery for a cask gauge chart — it’s a simple lookup based on cask size and depth. It takes 20 seconds per cask.

I use a basic stainless steel dipstick marked in centimetres and pints. It’s been accurate for five years and has cost me nothing in maintenance.

Temperature matters

Cask ale is meant to be served between 50–55°F (10–13°C). At warmer temperatures, the beer expands slightly; at colder temperatures, it contracts. A cask that reads 35 pints at 54°F will read marginally less at 58°F. The difference is tiny (usually less than 0.5 pint), but if your cellar is consistently warm, your measures will be off consistently.

Check your cellar temperature weekly and keep a log. Most variance is caused by temperature swings and forgotten partial kegs, not actual theft. A warm cellar creates phantom losses.

What about keg beers and spirits?

Keg beers (lagers, ciders, high-volume brands) come in stainless steel kegs that you can’t dip. You weigh them instead: the tare weight is stamped on the keg, and you subtract it from the total weight to get the volume of beer inside. Scales cost £20–£40 and are worth every penny.

For spirits and other open bottles, weigh them on the same scales. A 70cl bottle of vodka should weigh roughly 800g (accounting for the bottle). If it weighs 750g, you’ve lost about 50ml — either to over-pouring, spillage, or waste. Record the weight when you open the bottle and weigh it every day. It’s the fastest way to catch over-pouring before it becomes a pattern.

Why cask size matters for your margins

Your gross profit on draught beer is determined by cost per pint and selling price per pint. Get the pint count wrong, and your GP calculation is wrong.

A firkin costs roughly £55–£75 depending on the beer and brewery. If it yields 75 pints, your cost per pint is 73–100p. If you’re selling at £4.50, that’s a 77–82% GP on that line. But if the cask actually only yielded 70 pints because of head loss or measurement error, your real cost per pint is 79–107p, and your real GP is 75–82%. That’s a 2–3 point swing.

Over a week of 50 firkins, a 3-point swing is roughly £150–£200 in unseen margin loss.

The number that actually matters is wet GP by line, not a single headline stock figure. You need to know: cost per pint, actual pints yielded, selling price per pint, and total margin delivered. Most pubs can’t tell you any of those numbers with confidence.

This is why StockTap pub stock app tracks cask stock, temperatures, and line performance in one place. You log the cask size and dip depth, and it calculates the actual volume, flags temperature anomalies, and reconciles against till sales the same day. No more guesswork.

Common mistakes that cost you money

Mistake 1: Not dipping on arrival

A brewery will occasionally deliver a cask that’s not completely full — either a genuine accident or a partial order. If you don’t dip it when it arrives, you’ll be blaming your staff or your customers for losses that started before the cask even hit your cellar.

Mistake 2: Mixing up cask sizes in your head

You order a firkin but write it down as a pin in your spreadsheet, or you forget that you swapped out a kilderkin mid-week. Your stock count diverges from reality, your variances balloon, and you can’t find the error because you’ve lost track of which casks are which. Use a permanent marker to write the cask size and the date opened on every cask you connect. It takes 10 seconds and prevents hours of confusion later.

Mistake 3: Assuming the brewery’s pint yield

Breweries print a guide yield on their delivery notes (usually 72–80 pints per firkin depending on head loss assumptions). But your actual yield depends on your cellar temperature, your line cleaning, your pour consistency, and your wastage. A cask that yields 76 pints in one pub might yield 72 in another. Measure your actual yield by dividing the dip volume by the number of pints recorded on your till. Do this for five weeks and you’ll have a real average yield for each beer. Use that number, not the brewery’s estimate.

Mistake 4: Forgetting partial kegs

You get to the end of the week, you count stock, and you find a pin of bitter in the corner that’s been sitting there for three weeks because someone switched the line. You write it down as a full pin, reconcile against till data, and suddenly you show a massive variance. The partial keg isn’t missing — you just forgot it existed. Keep a live spreadsheet or app log of every cask you open and every cask you rack (disconnect). Update it as you go, not at the end of the week. Most pubs that move from a messy spreadsheet to a disciplined count claw back 1–2 GP points within a couple of months, largely by catching these forgotten partials.

Mistake 5: Not reconciling till data against stock on the same day

You do your stock count on Monday morning. You reconcile against till data from the previous week on Tuesday. By then, you’ve lost the detail: what sold on which day, whether any staff shortages created unusual patterns, whether a burst pipe or spillage happened. Reconcile the same day. If you dip casks at closing time on Sunday night and reconcile against the week’s till data on Monday morning, you can spot anomalies while they’re still fresh.

Building a weekly cask check routine

You don’t need a complicated system. You need consistency and the right tools.

What you need

• A calibrated dipstick (£10–£15)
• A set of kitchen scales for kegs and spirits (£20–£40)
• A permanent marker
• A notebook or app log
• A cask gauge chart from your brewery
• Your till reports from the week

The routine

Every Sunday evening (or your quietest shift):

1. Dip every active cask. Record the cask size, depth reading, and calculated volume. Write the depth on the cask with a marker.
2. Weigh every keg and open spirit bottle. Record the weights in your log.
3. Note any partial kegs or low-stock items. Flag any cask that’s running low so you can order replacement stock.
4. Record the cellar temperature. Note any variance from the previous week.

Every Monday morning:

1. Pull till reports for the previous week. Calculate pints sold per line (total revenue divided by selling price per pint).
2. Compare till pints against dip volumes. The difference is your variance. A variance under ±2% is acceptable; over ±3% needs investigation.
3. Investigate anomalies. Was a line not cleaned properly? Did a cask run out mid-shift? Was a pint measure tampered with? Did someone forget to ring a round? The answer is usually boring (forgotten wastage, spillage, or measurement error), but you’ll only know if you ask.
4. Record the results in a weekly P&L. Your wet GP by line should be consistent week to week. If it swings, your measurement or your pricing is off.

That’s it. 45 minutes a week. It catches losses before they compound, and it gives you real numbers to manage against.

I used to run this routine with a notebook and a basic spreadsheet. It worked fine. But once I moved to SmartPubTools, the reconciliation happened automatically: I logged the dipstick reading, the app calculated the volume, pulled the till data, and flagged variances in real time. It eliminated the spreadsheet shuffle and the mental arithmetic.