How to weigh a keg for stock
Last updated: 29 June 2026
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Most pubs are losing money on draught stock every single week without realising it, and a set of bathroom scales is often all that stands between profit and waste. If you’re not weighing your kegs at least once a week, you’re flying blind — and the brewery stocktaker will never catch it for you because they’re counting movement, not loss. Weighing a keg for stock is the fastest, most reliable way to measure what’s actually in your cellar and spot shrinkage before it becomes a habit. You don’t need fancy equipment or a degree in physics; you need a method that takes five minutes and gives you a number you can trust. This guide shows you exactly how to weigh a keg for stock, what you need, what to measure against, and why most pubs get this wrong.
Key Takeaways
- A 1% stock loss on wet sales quietly costs a typical pub £3,000–£5,000 a year, and most of it is hidden in draught wastage and over-pouring, not theft.
- The most effective way to measure draught stock loss is to weigh each partial keg the same day, record the weight alongside till data, and check for variance within 48 hours.
- You need only three things: a set of digital bathroom scales, a notebook or spreadsheet, and 15 minutes per week — no app required, but accuracy depends on consistency.
- Brewery stocktakers measure movement, not loss; they will never catch cellar shrinkage because it’s invisible in their paperwork.
Why weighing kegs matters more than you think
Spirits hide losses in over-pouring (a free-poured 25ml is often 32–35ml), draught hides it in poor cellar temperature and bad line cleaning waste, and most stock ‘theft’ is actually measurement error and forgotten wastage. The brewery will send a stocktaker to count full and empty kegs, but they’re checking against a delivery note. They don’t measure what’s left in a half-empty keg, and they have no way of knowing whether you’ve lost a pint to a slow leak, wastage from changeovers, or a tap left running. That’s on you.
The number that actually matters is wet gross profit by line, not a single headline stock figure. If your cask ale is showing a 2-pint loss per week, your temperature probe is probably broken or your line cleaner isn’t doing their job. If it’s 10 pints, someone is stealing or pouring with a bucket. Weighing tells you which one. A 1% stock loss on wet sales quietly costs a typical pub £3,000–£5,000 a year, and it’s almost never caught because nobody is looking week to week.
At my own pub I was running stock on a tangle of spreadsheets and still losing track of partial kegs and spirit measures. I built a simple count routine around a dipstick and a set of scales, and the weekly variance went from guesswork to a number I could trust within a fortnight. That’s when I saw the real loss — not in the headline figure, but in the draught lines. A faulty regulator was costing me about 4 pints a day of head and spillage. Once I fixed it and started weighing weekly, I clawed back roughly 1.5 GP points within two months.
What equipment you actually need
You don’t need industrial scales or software. The equipment is deliberately simple because the job is simple:
- Digital bathroom scales — accuracy to 100g (0.1 kg) is enough. They cost £15–£30 and are available everywhere. Mechanical scales are fine if you can read them clearly; digital is just easier in a dark cellar.
- A notebook or spreadsheet — record the date, keg code, product name, weight, and till sales for that day. Nothing fancy. A pen and paper in your cellar is fine; a simple spreadsheet is better because you can spot trends.
- A calculator or mobile phone — to work out weight loss against pints sold (see step 4 below).
- Optional: a StockTap pub stock app — if you’re tracking multiple lines or want a permanent record, this centralises your cellar weights, till data, and variance calculations in one place, no spreadsheet wrestling.
That’s it. You do not need a purpose-built cellar scales, a barcode scanner, or a monthly subscription to a hospitality system. If you already have a set of bathroom scales in the house, you’re ready to start now.
Step-by-step: how to weigh a keg properly
1. Prepare the scales
Place the scales on a flat, hard surface in your cellar. Not on carpet, not on a slope, not next to a vibration source like a cooler fan. Flat concrete or tile. Zero the scales (press the tare button if it has one, or note the reading if it doesn’t). If the scales have a battery, check it’s not low.
2. Record the keg details
Write down or enter into your tracking sheet:
- Today’s date
- Keg code or product name (e.g., “Guinness 30L #4”, “Peroni 20L #2”)
- When the keg was tapped (if you’re weighing a partial keg)
- The till reading for that product today (or the total sold since it was tapped if it’s a partial)
3. Lift the keg onto the scales
This is the part that surprises people. Kegs are heavy — a full 30-litre stainless steel keg can weigh over 60 kg. You might need to place it on its side on the scales, or use a small ramp if your scales have a low lip. The keg must be stable and the weight must register fully. Take the reading and write it down. If the scales flicker, wait 3–4 seconds for the digital reading to settle.
4. Weigh immediately after service, not before
Always weigh a partial keg at the end of the day, ideally just after last orders or within 2 hours of the pub closing. This captures the true state of what’s in the keg at that moment, and you can reconcile it against the till sales from that day. If you weigh a keg at opening time, you’re guessing how much has been sold and lost in the hours since.
Reading the weight and spotting stock loss
Once you have a weight, you need a baseline to compare it to. The calculation is straightforward but requires one piece of information: the weight of the keg when it was full.
Get a baseline weight
When you tap a new keg, weigh it immediately. Record this as the “opening weight.” For example:
- Guinness 30L keg, tapped Monday 15 June. Opening weight: 59.2 kg.
If you don’t have a baseline (e.g., if the keg was already in use when you took over), ask the brewery or call the keg manufacturer. They will give you the tare weight of an empty keg plus the nominal litres. A full 30L keg is roughly 30 kg of liquid plus the keg weight (typically 28–32 kg depending on material).
Calculate loss
Weighing the keg five days later shows 54.8 kg. Loss = 59.2 − 54.8 = 4.4 kg. At approximately 1 kg per litre for beer, that’s 4.4 litres sold or lost.
Cross-check this against the till. If the till shows 18 pints of Guinness sold in those five days (18 pints = roughly 10.2 litres), then you’ve lost 10.2 − 4.4 = 5.8 litres unaccounted for. That’s significant. It’s either in the lines (normal wastage from changeovers), in spillage, in over-pouring, or in the sink. Once you see the pattern, you can investigate which one.
Build a variance log
Track variance week on week. If a line is consistently showing a 10–15% loss, that’s normal for draught (head, spillage, line flushing). If it’s 25%+ in a week, or if it’s getting worse, that’s a problem. Most stock loss is actually measurement error and forgotten wastage, not theft — but you can’t know that without the data.
Common mistakes that kill accuracy
Weighing at different times of day
If you weigh Monday morning and Wednesday evening, you’re not comparing like with like. The keg has been open and potentially exposed to different pressures and temperatures. Weigh at the same time each week, ideally end of service.
Forgetting to zero the scales
If your scales read 0.3 kg when empty and you don’t reset them, every reading will be 300g high. Over a month, that’s a whole pint of phantom loss. Always zero before weighing.
Not accounting for line volume
When you first tap a keg and connect it to a 20-metre run of line, the first 2–3 pints go to fill the tube, not the glass. If you’re weighing a keg two hours after tapping it, the line fill is already accounted for in the weight. But if you’re comparing a keg that’s been on line for two weeks against a freshly tapped one, the variance will look wrong. Document when each keg was tapped.
Scales not on level ground
A slope of even 5 degrees will throw the reading out by 5–10%. Your cellar might be on a slope. Use a spirit level and shim the scales if needed.
Not recording till data at the same time
If you weigh the keg on Tuesday morning but don’t record till sales until Wednesday, you’ve lost a day of sales data. The variance is now useless. Reconcile within the same 24 hours.
How often to weigh and when to investigate
Weekly is the minimum
A proper weekly line check catches stock loss before it becomes a habit. Pick one day — say, Thursday evening after service — and weigh all your open draught lines. It takes 15 minutes. Most pubs that move from a messy spreadsheet to a disciplined count claw back 1–2 GP points within a couple of months.
When to dig deeper
If a line is showing:
- 10–15% variance over a week: Normal for draught. Document it and move on.
- 20%+ variance: Check the regulator pressure, inspect the line for leaks, ask the line cleaner if they’ve done a full clear-out recently.
- Variance that’s getting worse week on week: You have a slow leak in the line, a faulty tap, or a temperature problem. Call your supplier or a line specialist.
- A sudden spike in variance on one keg: Something happened that day — a dropped keg, an open tap left running, a line explosion. Investigate that day’s service notes and till void records.
Compare against historical data
After four weeks, you’ll have a baseline. Guinness might run at 12% variance, cask ale at 18%, and lager at 8%. Once you know your baseline, anything outside it is a signal. If Guinness suddenly jumps to 22%, that’s a problem worth investigating. If it stays at 12%, that’s just the cost of doing business.
Frequently Asked Questions
Do I need special scales to weigh a keg?
No. Standard digital bathroom scales with 100g accuracy are sufficient. They cost £15–£30 and are accurate enough to track variance week on week. Mechanical scales work too, but digital is easier to read in a dark cellar. You don’t need industrial scales unless you’re running a large multi-site operation.
Can I just use my EPOS till to track stock instead of weighing?
Your EPOS tells you what sold. It doesn’t tell you what’s in the keg or what was lost to spillage, over-pouring, and wastage. Weighing fills that gap. You need both: till data to confirm the sale, and keg weight to confirm what left the cellar. Together, they show you the loss.
How accurate does the weight need to be?
Accuracy to 100g (0.1 kg) is more than enough. Over a week, you’re tracking litres of loss, not grams. A variance of 100g is noise. What matters is tracking the trend: is this line getting worse, staying stable, or improving?
Won’t the brewery stocktaker catch the loss when they collect the keg?
No. The brewery counts full and empty kegs against the delivery paperwork. They’re not measuring what’s left in a half-full keg, and they have no way to know if you lost 2 pints to a leak or 2 pints to spillage. By the time the keg leaves your pub, the loss is historical. Weighing tells you about it in real time, so you can fix it.
What if I only have time to weigh kegs once a month?
Once a month is better than never, but you’ll miss weekly spikes and slow creeps in variance. A leak that costs you 4 pints a week stays hidden for 30 days under monthly counting. Weekly weighing takes 15 minutes and catches problems within days. If time is the barrier, the answer is to make it routine, not to skip it. Many operators who say they don’t have time find they do once they start.
Recording weights in a notebook works, but a spreadsheet or app catches patterns faster.
If you’re tracking multiple draught lines, the manual maths gets tedious, and trends hide in static. SmartPubTools built StockTap pub stock app to centralise cellar weights, till reconciliation, and variance tracking in one place. Record the weight, plug in the till sales, and the app calculates loss instantly. One-off cost, no subscription, works on any device. No money-back guarantee needed — if you’re serious about stock loss, this pays for itself in one recovered GP point.
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