Stockout
A stockout occurs when sellable inventory is unavailable to meet demand for a specific item at the required time and location.
What is Stockout?
An ecommerce stockout can occur at the variant, warehouse or channel level. The store may hold plenty of inventory overall while lacking the exact size or item a shopper wants. Availability is specific to the demand being served.
Physical stock is not always sellable stock. Units can be reserved, damaged, awaiting quality checks or positioned in a warehouse that cannot fulfill the order. A positive physical count therefore does not guarantee availability.
The popular size sells out first
A shoe store has 120 pairs across a style, but zero sellable pairs in size 8. Twelve shoppers request that size before replenishment. The size-8 stockout exists even though the style has inventory. The twelve requests do not automatically equal twelve permanently lost sales: some customers may wait or choose another size or product.
How to interpret it
A stockout is an availability event, not a revenue-loss formula. Its effect depends on customer behavior: an order may be delayed, substituted, backordered or lost. Estimate the economic impact with evidence rather than multiplying every missing unit by list price.
Recorded sales during an unavailable period can understate demand. If the site prevents checkout when stock reaches zero, the sales history no longer observes everyone who would have bought. That matters when using past sales to forecast replenishment.
Stockouts may arise from demand surprises, supplier delays, inaccurate inventory records or stock allocated to the wrong location. The event identifies the failure to meet demand but does not identify the cause.
Measure duration and scope carefully. A two-hour outage for one variant is different from a week-long outage for the entire product range. A stockout rate needs a denominator such as SKU-days, order lines or demand units; these versions are not interchangeable.
Backorders are a response, not available stock
Accepting a backorder allows the store to record demand while promising later delivery. It does not remove the current shortage. Keep promised dates and eventual cancellations visible when assessing how much demand was retained during the stockout.
Common mistakes
Treating zero recorded sales as zero demand
Unavailable stock can prevent sales from being recorded. A quiet sales report may be hiding an availability constraint.
Using total inventory as proof of availability
Only the requested sellable variant in a usable location can meet the specific demand. Aggregate stock can conceal the shortage.