Fill Rate
The share of demand you actually fill from stock.
Definition
Fill rate is the percentage of customer demand you satisfy from available stock, calculated as units shipped divided by units ordered over a period. A 95% fill rate means you fulfilled 95 of every 100 units customers wanted; the missing 5 were lost or delayed because you were out of stock.
Why fill rate matters for an FBA seller
On Amazon a stockout does not become a backorder, it becomes a lost sale and often a lost rung on the rankings. Fill rate is the scoreboard for how often you are actually capturing the demand you worked to create. The gap between 100% and your fill rate is revenue that walked to a competitor, plus the ranking momentum that walked with it.
Fill rate vs service level vs sell-through
Fill rate measures demand met. Service level measures the probability you avoid a stockout during a replenishment cycle, and it is the dial you turn when you size safety stock. Sell-through measures how fast stock moves relative to what you hold. They are related but answer different questions, so do not use them interchangeably.
How fill rate connects to your restock decisions
Amazon does not report fill rate as a native metric, so you approximate it from units ordered versus units shipped over a period. Most sellers aim for a service level in the 95% to 99% range, accepting that the last percentage point of fill rate is the most expensive inventory you will ever hold.
Chasing a perfect 100% fill rate means burying cash in overstock and paying storage fees for the privilege. The right target balances holding cost against the cost of a lost sale, set per SKU through a service-level-driven safety stock rather than one blanket rule for the whole catalog.
Related terms
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