Stockout: what running out actually costs a small store
A stockout is when a SKU hits zero sellable units and a customer who wants it cannot buy it. This page defines the term, shows the arithmetic that quietly produces one, and lists the related words you will meet next.
What a stockout is
A stockout is the point at which a SKU has no sellable units left, so demand arrives and cannot be filled. The word is warehouse shorthand for what most merchants say plainly: we ran out.
A stockout is measured per SKU, not per store. You can have a healthy overall inventory value and still be out of the one variant that carries your revenue. The size of a shelf, in days rather than units, is the number that matters: a SKU with 400 units and a slow trickle of orders is fine, and a SKU with 30 units selling six a day is five days from empty.
The arithmetic, worked
Say one scent of candle sells six units a day. You have 30 left, which is five days of cover. Your supplier's lead time is 21 days from purchase order to received stock. Even if you place the order this afternoon, the SKU is at zero on day five and stays there for sixteen days. Nothing went wrong in that story. Nobody was careless. The order was simply placed after the window closed rather than before it, and the window was 21 days wide.
What running out actually costs
We are not going to hand you a percentage. The honest answer is that the cost depends on your margin, your traffic mix and how loyal the buyer was, so treat these as the places the money leaks rather than a figure to put in a spreadsheet.
- Lost margin on units you would have sold. The demand existed and was turned away.
- Ad spend that landed on a sold-out page. Traffic you paid for converts at zero.
- A customer who found a substitute. They may come back. They may now buy that scent from someone else by default.
- Rush freight and split shipments to close the gap, which eat the margin on the units that do arrive.
- Attention. Chasing a supplier for an emergency order is the most expensive hour in the week.
A stockout is usually not a demand problem or a supplier problem. It is a timing problem, and timing problems are the kind you can fix with a number you calculate in advance.
Related terms you will meet next
- Reorder point. The stock level at which you must place an order to receive it before you hit zero. Built from sales velocity and lead time.
- Lead time. The days between sending a purchase order and having sellable stock on the shelf, including freight and receiving. You supply this per SKU; nobody can infer it for you.
- Sales velocity. Units sold per day, averaged over a window such as 7, 14 or 30 days. Short windows react fast and overreact to spikes; long windows are calmer and slower.
- Days of inventory remaining. Current stock divided by sales velocity. The most scannable health metric per SKU.
- Safety stock. A deliberate buffer held on top of the reorder point to absorb a demand spike or a late supplier.
- Backorder. Accepting an order you cannot ship yet. It keeps the sale but transfers the wait to the customer.
- Oversell. Selling units you do not physically have, usually because the recorded count drifted from the shelf count.
For the arithmetic that turns velocity and lead time into an actual order date, see the guide on when to reorder in this pillar.
Questions
Is a stockout the same as being out of stock?
Yes, in everyday use. Stockout is the operations word for the same event, and it is usually counted per SKU and per day so you can see how long you were dark rather than just that it happened.
What causes stockouts?
Almost always the gap between lead time and the stock on hand at the moment you notice. Demand rising faster than your last average, a supplier slipping a week, or simply checking the SKU list on the wrong Tuesday will all produce the same outcome.
Is a stockout ever acceptable?
On a tail SKU you are deliberately winding down, sometimes yes. On a hero SKU that carries your revenue, it is worth engineering against, because the cost of a buffer is a known holding cost and the cost of running out is not.
How do I know how close I am to a stockout?
Divide current stock by your average daily sales to get days of inventory remaining, then compare that number to your supplier lead time. If days remaining is smaller than lead time, you are already late.
Do I need an app to avoid running out?
No. A spreadsheet with velocity, lead time and a reorder point per SKU works fine. The failure mode is human: it only protects you on the days you remember to open it and refresh the numbers.
What is the difference between a stockout and a reorder point?
The stockout is the event. The reorder point is the line you set ahead of it, far enough back that an order placed at that line lands before the shelf empties.