Regauging casks: when to do it, how it works, and what the book-vs-actual gap means

Every cask in a Scotch warehouse is slowly losing alcohol. Your stock ledger, meanwhile, usually carries the figure the cask was filled at years ago. A regauge is the moment those two numbers meet — and the difference between them matters for your HMRC returns, your vatting yields, your insurance and your sale prices.

This guide covers when to regauge, how the measurement works, and how to record the result so your stock still balances. It is general guidance, not tax advice.

OLA and RLA: the two numbers every cask carries

When a cask is filled, you record the volume and strength going in. A hogshead filled with 250 litres at 63.5% ABV holds 250 × 0.635 = 158.75 LPA. That is its original litres of alcohol (OLA) — the book figure.

Years later, evaporation has taken both volume and (usually) strength. A regauge might find 228 litres at 61.8% ABV: 228 × 0.618 = 140.9 LPA. That is the regauged litres of alcohol (RLA) — the actual figure.

The 17.85 LPA between them did not vanish from your paperwork's point of view. It is a loss in storage, and until you regauge, your books are overstating your stock by that amount.

When should you regauge?

There is no HMRC rule saying "regauge every N years", but there are moments where working from the book figure is asking for trouble:

• Before a vatting or bottling. Your recipe, your expected yield and your duty planning all depend on real LPA, not the fill figure. This is also the moment the storage loss crystallises on your W1 return.
• Before selling a cask. Brokers and private buyers price on RLA. A sale quoted on OLA will be renegotiated the moment the buyer regauges.
• Before insuring or revaluing stock.Insurers and auditors want current figures, not 2014's.
• On a rolling cycle for long-maturation stock. Many warehouses regauge a sample of older casks each year so the book figure never drifts too far from reality.
• When a cask looks wrong.A weeping stave, a soft hoop, a cask that sounds empty when it shouldn't — regauge it before the loss gets worse.

How a regauge is actually done

Two methods dominate in Scotland:

Weight and strength.The cask is weighed, the tare (empty) weight of the cask is subtracted, and the net weight of liquid is converted to volume using the spirit's density at its measured strength and temperature. Strength comes from a sample measured with a calibrated density meter or hydrometer. This is the most accurate method and the standard for sales and bottling.

Dip and strength (ullage).A dip rod through the bung measures the depth of liquid, which is converted to volume from the cask's dimensions. Faster, less accurate — fine for monitoring, not ideal for pricing a sale.

Either way, the output is the same pair of numbers: bulk litres and ABV, multiplied together to give RLA. Record the method, the date, the temperature and who did it — if HMRC or a buyer queries the figure later, the measurement context is what makes it defensible.

A worked example

A butt filled in 2016:

• Fill: 500 litres at 63.5% ABV → OLA = 317.5 LPA
• Regauge in 2026: 452 litres at 60.9% ABV → RLA = 275.3 LPA
• Storage loss over ten years: 317.5 − 275.3 = 42.2 LPA (about 13.3%, or roughly 1.3% a year — unremarkable for Scotland)

If this cask now goes into a vatting, the vatting's input is 275.3 LPA, not 317.5. The 42.2 LPA goes to the W1 as a loss in storage. Anything lost between the regauge and what actually comes out of the vatting — pipework, filtration, samples — is a separate loss in operations. Keeping those two apart is one of the most common W1 mistakes we see.

What to do with the book-vs-actual gap

1. Update the cask record to the RLA, keeping the OLA and the full regauge history. Never overwrite history — the trail from fill to today is exactly what an auditor or buyer wants to see.
2. Post the difference as a storage loss in the W1 period the regauge happened, with the cask reference attached.
3. Sense-check the rate. Scottish maturation losses typically run around 1–2% of alcohol per year. A cask losing 5% a year has a physical problem; a cask that gained alcohol has a measurement problem (or a very dry warehouse concentrating the spirit — it happens, and it raises its own questions about volume loss).
4. Investigate outliers before filing. HMRC expects losses to be reasonable and explicable. A pattern of unusual losses with no investigation behind it is what turns a routine visit into a long one.

Where regauging goes wrong

1. Pricing or vatting from OLA. The most expensive mistake: yields come up short, duty estimates are wrong, and cask sale negotiations reopen.
2. Overwriting the book figure with no audit trail. The loss disappears from view and the W1 stops reconciling to the cask ledger.
3. Posting the loss in the wrong period. A regauge done on 30 September but keyed on 3 October needs a consistent rule for which month it belongs to.
4. Mixing temperature bases. Volume and strength move with temperature; comparing a cold-warehouse dip to a lab strength at 20°C without correction skews the RLA.
5. Forgetting the sample. The litre you drew to measure strength is itself a loss. Small per cask, real at scale.
6. No tare weight on record. Without the empty cask weight, weight-based regauging turns into guesswork.

How Provenate handles regauging

Provenate is distillery management softwarethat keeps each cask's full measurement history in one record:

• OLA preserved, RLA current. Every regauge is a dated event on the cask — method, volume, strength, temperature, operator — and the current RLA is what vattings, sales and reports use automatically.
• Losses posted for you. The book-vs-actual difference flows to the correct W1 period as a loss in storage, traceable back to the individual cask.
• Storage and operational losses kept apart. When a regauged cask is vatted, Provenate separates the maturation loss from the operation loss, the way HMRC expects to see them.
• Outliers flagged. Casks losing alcohol faster than their peers surface for investigation before they surface in a return.

Want to see your cask ledger reconcile itself? Book a demo.

Official sources

• Excise Warehousing: Excise Warehouse Return (W1) form and notes
• Alcoholic products technical guide
• Receive goods into and remove goods from an excise warehouse (Excise Notice 197)