The most stringent measurement of fill rate to support product availability is:

According to the APICS CSCP - Supply Chain Management Certification, customer fill rate is the most stringent measurement of fill rate to support product availability. Fill rate is a measure of how well a supplier or a distribution center satisfies customer demand for a product or a service. Customer fill rate is calculated as the percentage of customers who receive all the items they ordered in the quantity they ordered within the agreed time frame. Customer fill rate reflects the overall performance of the supply chain in meeting customer expectations and satisfaction.