- OOS Rate refers to your Out of Stock Rate. In Stock % (over time) is the percentage of time the product has available inventory over the period. For example, if a product was in stock for 28.1 days out of the last 30 days, the In Stock % would be 28.1 / 30 = 93.7%. Your Out of Stock rate would then be the opposite of this, that is, the product was out of stock for 1.9 days out of the 30 days giving you 6.3% Out of Stock Rate.