Sales Velocity
Units sold per day. The base rate behind every restock calculation.
Definition
Sales velocity is the average number of units a product sells per day, measured over a recent trailing window. It is the base rate every replenishment calculation runs on: days of supply, the reorder point, and safety stock all start from how fast a SKU actually moves.
Why sales velocity matters for an FBA seller
Velocity is the number that turns an inventory count into a plan. A SKU with 800 units on hand is either two weeks of cover or two months of cover, and the only thing that decides which is how many units a day it sells. Get velocity right and every downstream number (days of supply, reorder point, order quantity) lands in the right place. Get it wrong and all of them inherit the error.
It is also the metric most sensitive to how you measure it. A 7-day window reacts fast but whipsaws on a single good or bad day. A 90-day window is stable but slow to notice that a SKU is taking off or fading. The right window depends on the product, and blending a few windows usually beats trusting any single one.
Trailing velocity is backward-looking, and demand is not flat
The simple version of sales velocity divides recent units sold by the number of days in the window. That works for a product that sells the same amount every week forever, and almost no Amazon SKU does. Seasonality, promotions, ranking changes, competitor stockouts, and price moves all bend future demand away from the trailing average, often sharply.
Planning a Q4 buy off a flat October velocity is the classic version of this mistake: the trailing number looks comfortable right up until peak demand arrives and the SKU is gone in days. A forward-looking velocity that accounts for where demand is heading is what keeps the reorder point honest when sales are trending.
How sales velocity connects to your restock decisions
Velocity feeds two separate questions. It sets when to reorder, because the reorder point is velocity multiplied by lead time plus safety stock. And it sets how much to reorder, because order quantity is just velocity projected across the time the next batch has to cover.
Because velocity moves with seasonality and promotions, it has to be recalculated continuously, not read once a month off a stale report. Track it per SKU rather than as a blended account average, since the account number hides the fast movers that are about to run dry and the slow movers quietly aging toward storage fees.
Related terms
See live sales velocity per SKU
Inventory Hero tracks each product's real velocity and trend, the input behind every reorder point and forecast it generates for you.
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