How to Measure a Partial Keg

Last updated: 26 June 2026

Most pub operators have no idea what’s actually in their partial kegs on any given Tuesday. You pour thousands of pints a week but when it comes to the half-full cask sitting in the cellar, you’re left guessing—and that guessing habit costs you money. A 1% stock loss on wet sales quietly costs a typical pub £3,000–£5,000 a year, and most of that loss hides in measurement error and forgotten wastage rather than theft. The good news: measuring a partial keg accurately takes about ninety seconds, and when you do it consistently every week, your stock variance shifts from a wild guess to a number you can actually trust.

In this article, I’ll walk you through the exact method I use to measure partial kegs at my own pub—the equipment you need, the measurement technique that works, and how to reconcile what you find against your till data so you catch losses before they compound.

Why Partial Keg Measurement Matters

The most effective way to protect your wet GP is to measure partial kegs every single week. When you ignore partial kegs between deliveries, you’re flying blind. Your till tells you what you sold. Your physical stock tells you what’s left. The gap between the two is your profit or your loss.

I spent years running stock on a tangle of spreadsheets and still losing track of partial kegs and spirit measures. The variance I was seeing was enormous—sometimes 3% to 4% worse than it should have been—but I had no way to pinpoint where the loss actually was. Was it the bitter? The lager? Waste? Over-pouring? 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 number then told me exactly which lines needed attention.

The operators who move from a messy spreadsheet to a disciplined weekly count usually claw back 1–2 GP points within a couple of months. That’s the difference between breaking even on a quiet Tuesday and actually making money.

The Equipment You Actually Need

You don’t need fancy kit. You need three things: a calibrated dipstick, a set of scales, and a record sheet (paper or digital—it doesn’t matter, as long as you fill it in the same day).

Dipstick

A calibrated dipstick is a long ruler marked in litres, usually to the nearest 0.5 litre. It measures the depth of liquid in a cask or keg. Most breweries will supply one free, or you can buy a stainless steel one for £10–£20. The key is that it has to be calibrated for the specific barrel size you’re measuring—a 9-gallon cask dipstick reads differently than a 11-gallon or a modern slim keg. Ask your brewery rep to confirm you have the right one.

Scales

A simple set of digital kitchen scales (£15–£30) or a small platform scale works. You’re weighing open bottles or keg couplings to check for product loss. If a keg coupler feels lighter than it did three days ago but you’ve sold fewer pints than expected, something’s wrong—and the scales will confirm it.

Record Sheet

A notebook, a spreadsheet, or a dedicated stocktaking app. What matters is that you record the same information every week in the same format: keg or line name, dipstick reading in litres, date, time, and any notes (e.g. “line cleaned”, “keg changed”, “waste noted”). This becomes your evidence trail. If your variance is consistently 0.5 litres high on your IPA, you’ll spot it after four weeks. That’s actionable.

How to Measure a Partial Keg: Step by Step

The actual measurement takes less than two minutes per keg.

Before You Start

• Make sure the keg is standing upright and hasn’t been moved for at least five minutes (liquid settles; if you measure while it’s still moving, the reading bounces).
• Check the keg is at cellar temperature. If you’ve just moved it from a warm room, wait. Temperature affects volume.
• Have your record sheet or app open and ready.

The Measurement

Insert the dipstick slowly and vertically into the top of the keg until it touches the bottom. Don’t ram it. The stick should slide down easily. Once it stops, hold it steady and read the number where the liquid level sits on the scale. That’s your remaining volume in litres. Note it down immediately with the date and time.

If the keg has a narrow opening or a one-way valve, you may need to remove the coupler first. Do that gently—have a cloth or small bucket underneath to catch any drips. Once you’ve read the dipstick, replace the coupler and secure it. If you spot liquid on the floor or coupler, note the wastage in your record sheet (e.g. “0.3 litres lost during coupler check”).

Check for Leaks

While you’re in the cellar, look for puddles, damp patches, or drips around the keg. If a keg is losing more than a trace amount, it’s faulty and you need to call the brewery immediately. Leaks account for real losses, not measurement error.

Reconcile Against Till Data

The number that actually matters is not the dipstick reading—it’s the gap between what the dipstick says and what your till says you sold. Your till is usually accurate. Your physical stock usually lies. The difference is where your loss hides.

Pull your till sales report for that line over the past week. A pint of bitter at 568ml (standard) per pint means 10 pints = 5.68 litres. If your till says you sold 42 pints of bitter last week (23.9 litres) but the keg lost only 20 litres according to the dipstick, you have a 3.9-litre gap. That gap is waste, over-pouring, or stuck pints that were never rung up. It’s actionable.

Recording and Reconciling Your Measurements

Recording is where most operators fail. They take the measurement, note it vaguely, and then wonder why stock variance stays wild.

Use a consistent format every single week. Mine looks like this:

• Line name / Cask ID (e.g. “Marston’s Bitter Cask #247”)
• Date and time (e.g. “Tuesday 26 June 14:30”)
• Dipstick reading in litres (e.g. “18.5L”)
• Till sales for the period in litres (e.g. “sold 22.3L”)
• Variance in litres (e.g. “+2.8L unaccounted for”)
• Notes (e.g. “line cleaned Monday, keg changed Friday”)

Do this every week on the same day. I do mine on a Tuesday morning before service. After about four weeks, you’ll see patterns. Draught hides losses in poor cellar temperature and bad line cleaning waste. Spirits hide it in over-pouring (a free-poured 25ml is often 32–35ml). Most stock ‘theft’ is actually measurement error and forgotten wastage.

When you spot a recurring variance on a single line, that’s your signal to investigate: is the line pouring correctly? Is there a slow leak? Is the bar staff over-pouring? Did someone forget to ring in the waste? Use StockTap pub stock app or a simple spreadsheet to track this data over time. Either way, the weekly discipline is what matters.

Common Mistakes That Kill Accuracy

Measuring a Warm Keg

If a keg has been in a warm cellar or under a heat lamp, the liquid expands slightly. Measure only at cellar temperature (around 55°F / 13°C for cask ale). If you measure a warm keg, wait an hour and remeasure.

Forgetting the Coupler Loss

Every time you remove a coupler, a small amount of liquid is trapped in the coupler head. That’s typically 0.1–0.2 litres per change. If you change a keg on Tuesday and measure on Wednesday, your dipstick reading will be lower than expected because some product is still sitting in the old coupler. Note this in your record sheet as “coupler loss” so you don’t think the keg is leaking.

Not Accounting for Waste

When a line is cleaned, flushed, or a bad pint is poured down the sink, that’s real product loss. If you don’t note it, your variance will look like theft or error when it’s actually planned wastage. Teach your bar team to log waste—a notebook behind the bar takes thirty seconds to update.

Measuring at Different Times

If you measure Tuesday morning one week and Friday afternoon the next, you’re comparing different time windows. Stick to the same day and time every week. Tuesday 14:30 every week. That removes time-window variance from the equation.

Making Weekly Measurement Routine

The biggest obstacle to accurate measurement isn’t the equipment—it’s consistency. Most operators measure once and then forget for three weeks. By then, the numbers are too old to be useful.

Here’s how to make it stick:

• Pick a quiet day. Tuesday or Wednesday morning, before service, when you’re not fighting the lunch rush.
• Block the time in your calendar—treat it like a delivery that can’t be moved.
• Keep the equipment in one place—hang the dipstick and scales next to the cellar door so they’re visible every day.
• Record the data immediately. Don’t measure Monday, write it down Wednesday. The data quality collapses.
• Review the numbers every month. A spreadsheet or app shows you which lines are drifting. That’s where you focus next.

The reality is this: a weekly stocktake of partial kegs takes 15 minutes total for a typical pub. A monthly review of the data takes another 15 minutes. For 30 minutes a month, you get visibility into where your profit is actually going. Most operators waste that time gossiping or scrolling their phone, then spend months wondering why their stock variance is terrible.