Days-to-empty — knowing when each grade runs dry

Days-to-empty is the simplest useful number in fuel retail:

Days-to-empty = gallons on hand ÷ average gallons sold per day

If your regular tank holds 1,970 gallons and regular sells about 1,000 gallons a day, you have about two days. Not “plenty,” not “low” — two days, a number you can plan a truck around.

Why the average matters

Yesterday's sales alone lie to you: a rainy Tuesday and a holiday Friday are different animals. A rolling average of the last seven days of totalizer movement smooths the weather and the weekend into a pace you can trust — and it's computed from the same readings your daily reconciliation already collects. No extra work; the forecast rides on the book.

The 3-day line

Order lead time is the trap. If your distributor needs a day or two to get a truck to you — longer on weekends, longer in a storm week when everyone's calling — then “one day of fuel left” isn't a warning, it's an outage with a date on it. Alerting at about three days leaves room for the normal delay plus one bad break. Busy highway stores with same-day jobbers can run it tighter; rural stores on a two-day route should run it looser.

What a dry grade really costs

Not just the gallons you didn't sell. A customer who finds your regular pump bagged drives to the competitor — and takes the coffee, the lottery ticket, and the habit with her. Stations that ran dry during the Colonial Pipeline shutdown sued over exactly that: the filing noted the lost inside sales when the pumps went empty. Fuel brings the customer; the store makes the money; a runout taxes both.

Ordering the right amount

The companion number is ullage — the empty space in the tank. Order more than the ullage and the load won't fit; order far less and you're paying freight on air, twice as often. A practical default: order enough to fill to about 90% of capacity — full working stock, room for the load to land safely, and the fewest trips per gallon.

See days-to-empty for every grade — free book

More guides: Daily tank reconciliation · Fuel variance · The UST inventory log