An out-of-stock inventory buffer is a threshold below which a product is treated as sold out for sorting, even though it still has units left. With a buffer of 5, a product is demoted once stock falls to 5 or fewer. The point: the last few units are usually broken sizes and odd colors, so the product is effectively unbuyable for most shoppers long before it hits zero.
Why not just wait until stock hits zero?
Because “in stock” and “buyable by the shopper in front of you” diverge at the end of a product’s life. A tee with 4 units left might be one XS and three XXL. The product page says available, the collection page gives it a strong position, and the majority of shoppers who click it find their size greyed out. That is a wasted click in your most valuable real estate, and on a busy collection those wasted clicks add up to a quietly worse conversion rate. Demoting at zero fixes the empty case but not the nearly-empty case, which is more common and just as costly.
How big should the buffer be?
There is no universal number; size it to your catalog:
- Variant count. A product sold in 12 size and color combinations goes “effectively out” at a much higher unit count than a single-variant product. More variants, bigger buffer.
- Sales rate. Fast movers burn through a small remainder in hours, so a slightly larger buffer keeps the page from advertising stock that will be gone before the next re-sort. Days of inventory is a useful companion signal here.
- Restock behavior. If you replenish weekly, an aggressive buffer just hides products briefly. If sellouts are final, demote earlier.
What happens to buffered products?
They are pushed down, not removed: still findable for the shopper who wants exactly that last unit, just no longer occupying positions that should be selling. For the full mechanics, see our out-of-stock inventory buffer guide.
In Dynasort the buffer is a single configurable setting per recipe. Install it from the Shopify App Store or see how it works.