Back-bar buying math: liters, weeks of cover and dead stock
The shampoo-to-conditioner ratio your supplier ships is rarely the one your chairs actually consume.
Back bar gets bought the way petrol gets bought: when it runs low, somebody grabs more. That works until you count what is in the cupboard and find eleven liters of a conditioner nobody has opened since the rep left, next to an empty shelf where the shampoo should be.
Back bar is a cost of service, but it behaves like inventory. Treat it like inventory and it stops being a line item you cannot explain.
Start with consumption per service, not with the invoice
You cannot buy correctly until you know what a single service consumes. Measure it once, properly, and the number will hold for a year.
Pick a normal week. Weigh or mark a fresh liter of your main shampoo at the start of Monday and record the number of shampoo services the salon performs. At the end of the week, measure what is left. Divide.
Most salons land somewhere near these figures, but yours will differ — long-hair specialists and color-heavy salons consume very differently:
| Product | Typical use per service | Services per liter |
|---|---|---|
| Shampoo (single cleanse) | 15–20 ml | 50–66 |
| Shampoo (double cleanse) | 25–35 ml | 28–40 |
| Conditioner / rinse-out | 20–30 ml | 33–50 |
| Treatment mask | 30–45 ml | 22–33 |
The number that surprises most owners is the double cleanse. A salon that trains double cleansing on every color client is consuming close to twice the shampoo per head, and their annual back-bar spend reflects it whether or not anybody has done the arithmetic.
The ratio myth
Suppliers and reps often quote back bar in balanced pairs — a liter of shampoo, a liter of conditioner. Almost no salon consumes at 1:1. If you double cleanse and condition once, you are closer to 1.6 liters of shampoo per liter of conditioner. Buy in pairs for a year and you accumulate exactly the surplus conditioner you now have in the cupboard.
The same distortion applies to treatments. A mask that gets used on one client in six should not be ordered on the same cycle as the shampoo, however convenient it is to add it to the sheet.
Weeks of cover and the reorder point
Two formulas do all the work. Neither needs software.
Weeks of cover = units on hand ÷ average units consumed per week. It tells you how long you can trade without a delivery.
Reorder point = (average weekly consumption × lead time in weeks) + safety stock. It tells you the level at which to place the order.
Lead time is the part people get wrong, because they measure it from when they remember to order rather than from when the order is placed. If your distributor ships same-day on orders confirmed by 1:30 PM Mountain Time and ground transit to you is two days, your true lead time is under half a week — and your safety stock can be small. If you buy from a supplier that ships weekly on a set day, your lead time is up to nine days and your safety stock has to absorb that.
Worked example: a six-chair salon
Say the salon performs 210 shampoo services a week and double cleanses about half of them. Average consumption works out at roughly 22 ml per service, so:
- Weekly shampoo consumption: 210 × 22 ml = 4.6 liters
- Lead time: 0.5 weeks → lead-time demand = 2.3 liters
- Safety stock: one week of cover = 4.6 liters
- Reorder point ≈ 7 liters; order quantity: two weeks' cover, about 9–10 liters
That salon should be holding roughly 16 liters of its core shampoo at peak and reordering when it drops to seven. Not thirty liters because there was a case deal, and not two liters because nobody checked.
Liter economics against retail sizes
Liters are cheaper per milliliter, which is why they belong on the back bar. But there is a break point. A liter of a product used on one client a week will pass its practical freshness window before it is finished, and the saving evaporates.
The rule we give accounts: if a product does not consume a liter within twelve weeks, buy it in the retail size for back-bar use. You lose a few cents per milliliter and you gain a product that is still good when it is used, plus a bottle you can sell if the service demand disappears.
Where dead stock actually comes from
In our experience of restocking independents, back-bar dead stock has four sources, in this order:
- Range creep. Three shampoo families where one and a half would do. Every new family added is another set of slow-moving conditioners and masks.
- Promotional buys. A deal on quantity you cannot consume inside the season is not a discount, it is a loan you made to your supplier.
- Staff turnover. The stylist who championed a line leaves; the line stops moving that month. Ranging decisions should survive one resignation.
- Case-pack inertia. Ordering six because that is the case, when you need two. Ask whether your distributor will break a case — we do on the second order onward.
The quarterly cupboard count
Once a quarter, take everything out of the back-bar cupboard and put it on a table. Anything unopened and untouched for ninety days goes into one of three piles: use it (move it to the front and brief the team), sell it (retail it at a discount if the pack allows), or write it off and never order it again. Record which pile each SKU went to, because that record is your ranging decision for next year.
Key takeaways
- Measure consumption per service once, properly — every other number depends on it.
- Shampoo-to-conditioner is rarely 1:1. Double cleansing pushes it closer to 1.6:1.
- Reorder point = weekly consumption × lead time + safety stock. Short lead times mean less cash on the shelf.
- If a liter does not empty in twelve weeks, buy the retail size for back-bar use instead.
- Count the cupboard quarterly and record what you write off. That record is next year's range plan.