One row per tank, not per fuel
The most common mistake in a stock register is keeping it by fuel type rather than by tank. An outlet with two diesel tanks that records a single diesel line has already discarded the information that matters most — because a leak is a property of a tank, not of a product.
Pooling two tanks averages a drifting one against a sound one and produces a variance that looks unremarkable for months. Kept separately, the drifting tank stands out within weeks. The free stock register template is laid out one tank per sheet for exactly this reason. The same applies to a branded premium grade, which needs its own tank and its own register — see fuel grades explained.
The columns
Six columns, of which only two are measured. The rest are derived, and that is the point: nothing in a stock register should be adjustable to make the answer come out. The stock variance calculator does the arithmetic for a single tank-day.
There is a free Excel stock register with a month per tank and the variance computed down the column, if you would rather start from a file.
Opening stock is yesterday's dip, not yesterday's book stock
Carrying yesterday's book stock forward hides the variance instead of recording it — each day starts from a number that was already known to be wrong, and the error accumulates silently. Start from what you measured.
| Column | Where it comes from |
|---|---|
| Opening stock | Yesterday's closing dip for this tank |
| Deliveries received | Tanker log — litres decanted into this tank today |
| Litres dispensed | Sum of every nozzle drawing on this tank |
| Book stock | Opening + deliveries − dispensed. Computed. |
| Dip reading | Measured, through this tank's own calibration chart |
| Variance | Dip − book stock. Computed. |
Only opening stock and the dip are measured. The rest are computed.
A worked week
One tank, seven days. Individually every variance below is small. As a series, one of them is a problem.
| Day | Opening | Delivered | Dispensed | Book | Dip | Variance |
|---|---|---|---|---|---|---|
| Mon | 14,500 | 0 | 1,560 | 12,940 | 12,936 | −4 |
| Tue | 12,936 | 0 | 1,480 | 11,456 | 11,449 | −7 |
| Wed | 11,449 | 12,000 | 1,610 | 21,839 | 21,828 | −11 |
| Thu | 21,828 | 0 | 1,545 | 20,283 | 20,268 | −15 |
| Fri | 20,268 | 0 | 1,720 | 18,548 | 18,529 | −19 |
| Sat | 18,529 | 0 | 1,890 | 16,639 | 16,616 | −23 |
| Sun | 16,616 | 0 | 1,410 | 15,206 | 15,178 | −28 |
Tank T2, diesel. The variance is small each day and consistently negative and growing — which is the shape that warrants a tightness test.
Reading the variance
No single day in that table is alarming. Twenty-eight litres on a Sunday is 2% of nothing much, and any one of the four usual causes could produce it.
What is alarming is the shape. The variance is negative every day and larger every day, including on days with no delivery and across a range of throughputs. Evaporation does not do that — it tracks temperature and volume, not the calendar. Calibration drift does not do that either; it would be proportional to litres dispensed, and Sunday moved the least fuel of the week while showing the largest gap.
A variance that is negative and growing independently of throughput is the pattern that justifies a tank and line tightness test. Everything else on this page is bookkeeping; this is the reason to keep it.
- Small, negative, steady, worse in summer — evaporation. Record it and move on.
- Proportional to litres on one nozzle only — calibration drift on that dispenser.
- A step change starting on a date — a metering error, or a reading habit that changed.
- Negative and growing regardless of volume — test the tank and lines.
- Positive — almost always a delivery logged late or a dip taken before the tank settled. Fuel does not appear from nowhere.
Getting the dip right
Most surprising variances are measurement problems, not fuel problems. Five habits remove nearly all of them.
- Use the calibration chart supplied with that specific tank. A chart from a nominally identical tank invents a variance that is not there — the dip-to-litres calculator shows why a horizontal tank cannot be read linearly.
- Dip at the same time each day, when nothing is dispensing.
- Let the tank settle after a delivery before dipping — moving fuel reads high.
- A free tanker delivery log with the 15 °C correction built in is on the templates page.
- Dip the same point each time. Few tanks are perfectly level.
- Record water separately. Water sits under the fuel and reads as product on a plain dip, hiding a real loss.
Frequently asked questions
Is a stock register legally required?
Fuel outlets are subject to record-keeping obligations under the licences they hold, and what is required varies by state and by the terms of your dealership. Keep the register regardless of the minimum — its operational value is far greater than its compliance value.
How do I handle two tanks holding the same fuel?
As two rows. If nozzles can draw from either, you need to know which tank each nozzle actually drew from, or the dispensed column is guesswork for both. Where the manifolding genuinely makes that unknowable, record the pair as one unit and accept that you have lost the ability to isolate a problem to one tank.
What if the dip and the book agree exactly, every day?
Be suspicious. Exact agreement day after day usually means the dip is being written to match the book rather than measured — which converts the register from a check into a formality, and is worse than not keeping one, because it produces false confidence.
Should I convert the dip to 15 °C?
For the daily register, consistency matters more than the correction — dip at the same time each day and the temperature effect is largely constant. For a tanker delivery it matters a great deal, because warm fuel gauged in the tanker occupies more space than the same fuel once it cools in your tank.