After managing inventory long enough, you notice something one day: "100 units in stock" and "100 units available for sale" are not actually the same thing. The shelf in the warehouse really does have 100 units, but the moment you try to sell the last one, it cannot be found. Or it was damaged. Every store has had that experience.
That is why so many seasoned operators adopt the concept of an inventory buffer: subtract a few units from the actual count and use that lower number as the inventory customers see. It is a small move, but it is remarkably effective at preventing overselling and absorbing physical count discrepancies. In this article we walk through the technique sometimes called "hold back five," including how to express it in your sheet.
What is a buffer, and why do you need one?
A buffer is, literally, a cushion. In inventory management it refers to setting the publicly visible quantity slightly lower than the real quantity. For example, if you actually have 100 units, show 95 on Shopify. The remaining five sit as a reserve for emergencies, never visible to customers.
Why go to this trouble? There are several reasons. First, physical count discrepancies. No matter how meticulous you are, a few units of drift per month are inevitable. Returns processed late, mis-shipments, damage, loss—the causes vary, but in aggregate they add up to numbers you cannot ignore. The buffer absorbs them.
The other big reason is preventing overselling. The moment your sync app pushes inventory to Shopify and the moment a customer places an order are not always in lockstep. In the few minutes of sync lag, the last unit can be sold twice. A buffer prevents that kind of incident before it happens.
How much is reasonable?
So how many units should you actually hold back? It depends on the product and the size of your store, but there are useful rules of thumb. You cannot say "five" across the board; it is more realistic to vary the approach by product.
Rules of thumb by product type
Fast-moving consumables and popular products that take many orders per day deserve a larger buffer. If you sell more than 10 units a day, a buffer of 5 to 10 is a good starting point. For slow-moving high-ticket items or limited-run products, you can narrow the buffer to 1 or 2 units, because holding back too much turns into missed revenue.
- Fast-moving consumables: buffer of 5 to 10
- Standard products: buffer of 2 to 3
- High-ticket or limited items: buffer of 1 to 2
- Gift items (higher damage risk): buffer of 3 to 5
- Apparel with many size variants: 1 to 2 per SKU
Another thing not to forget is per-location thinking. If your store has multiple warehouses, the baseline is to set a buffer per location. If your main store and a branch have different inventory accuracy, it is reasonable to set a thicker buffer at the less accurate one.
How to express buffers in your sheet
If you keep your inventory source of truth in Google Sheets, you need a little structure to express the buffer. One typical approach is to separate it into its own columns.
- 01Column A: SKU
- 02Column B: actual stock (the figure confirmed at physical count)
- 03Column C: buffer (the reserve set per product)
- 04Column D: published stock (Column B minus Column C, computed by formula)
- 05Column E: what gets synced to Shopify (the value of Column D)
Set it up this way and the physical-count person only needs to look at column B, while the buffer manager only touches column C. The value actually pushed to Shopify is in column D. When you want to change the buffer, edit column C in bulk and column D recalculates automatically.
It is common to want different buffers by season—double during year-end shopping, half during the summer off-season. In that case, make the column C formula reference a parameter on another sheet and you can change buffers across every SKU in one line per season.
Subtracting the buffer at sync time
If you hold the buffer-subtracted figure as its own column in the sheet, your sync app simply points at that column. Conversely, even if your sync app has no built-in buffer feature, the math lives entirely in the sheet. That is a major benefit of keeping Google Sheets as your inventory source of truth.
Watch out for cases where the post-buffer value goes negative. If real stock is 3 and the buffer is 5, the result is minus 2. Send that to Shopify as is and you will either get an error or a value you did not expect. In your sheet, use a formula that floors at zero, like `MAX(0, ColumnB-ColumnC)`.
Buffers are not a "set it and forget it" thing; you tune them as you operate. Make a monthly habit of reviewing sales results, return rates, and trends in physical-count discrepancies, and adjust each product's buffer accordingly. Over time, the right numbers reveal themselves. Start by going with your gut—shipping and then iterating is enough.
An inventory buffer is not a flashy technique. But weigh it against the actual loss and apology cost of an oversell incident, and the peace of mind that comes from holding back a few units is significant. Adding a single column to your sheet is all it takes, so if you have not adopted this yet, give it a try.