How is on-shelf out-of-stock rate calculated?
The on-shelf out-of-stock rate is calculated by dividing the number of missing SKUs by the total listed SKUs and multiplying by 100: OOS (%) = (Number of missing SKUs ÷ Total listed SKUs) × 100 1. Out-of-stock describes shelf space in a brick-and-mortar store that is no longer filled by the intended article and is empty 2. Out-of-stock also covers any situation where a product is missing from the shelf when it is expected to be available 1.
A worked example
If a store carries 100 listed SKUs in a category and a shelf audit finds 92 SKUs physically present and visible while 8 SKUs are missing, the out-of-stock rate is (8 ÷ 100) × 100, or 8% 1. The same audit gives an on-shelf availability of (92 ÷ 100) × 100, or 92% 1. On-shelf availability and out-of-stock are directly linked, so as on-shelf availability improves, the out-of-stock rate decreases 1.
What the calculation depends on
- The level of aggregation, since retailers track availability at store level, category level, SKU level and for high-velocity SKUs 1.
- The distinction between stock availability, which reflects whether inventory exists in the system or store, and on-shelf availability, which reflects whether that inventory is present on the selling shelf 1.
- The reliability of the inventory system, because phantom inventory can show units in stock while a SKU goes weeks without appearing in a single store 3.
- Measurement frequency, since irregular measurement hides recurring stock gaps and slows response 1.
Most global FMCG and retail studies suggest a strong on-shelf availability rate falls between 95% and 98%, with anything below 95% starting to create measurable revenue impact 1.