The percentage of user requests, holds or acquisition‑related demands that are successfully satisfied from the collection (or collection network) within a specified time frame and according to an explicit fulfillment criterion (for example: same‑day fulfillment, fulfillment within X days, or provision of an acceptable equivalent).

Principle

Fill Rate operationalizes the collection’s capacity to meet demonstrated demand within operational service standards; it depends on both stock sufficiency and procedural performance (discovery, retrieval, lending policies, and supply networks).

Demonstration

Illustrative scenario: Situation — Over a quarter, patrons place 4,000 hold requests. Recognition — Library records show 3,200 of those were fulfilled from local holdings within the library’s target window. Action — The measured fill rate is 80% for the quarter; staff analyze unfilled requests by subject to guide purchases or interlibrary loan priorities. Consequence — Procurement and ILL policies are adjusted to improve responsiveness in poorly served areas.

Misapplication

Counting any provision (for example delivering a different edition or a citation) as fulfillment without qualifying acceptability conflates nominal fulfillment with genuine patron satisfaction; likewise, comparing fill rates without aligning the time window or fulfillment definition is misleading.

Consequence

Fill Rate influences user satisfaction, ILL workload, acquisition strategy and reputation: causal changes in fill rate stem from altering stock, discovery tools, processing speed or collaborative networks, and will shift operational workload and budget allocations accordingly.

Reversal

A high fill rate achieved by supplying substandard or irrelevant alternatives, or by outsourcing to expensive external sources, may mask underlying collection deficiencies and create unsustainable costs; in another reversal, deliberately low fill rate may be accepted for restricted collections where mediated service is policy.

Boundary

Clearly within: requests that are met by supplying the requested item (or an institutionally defined acceptable equivalent) within the stated timeframe. Boundary case: items fulfilled by expedited purchase rather than existing holdings — considered fulfillment if the policy counts purchases. Clearly outside: requests that result only in advice, citations, or long‑term acquisition plans beyond the fulfillment window.

Semantic Tension

Réactivité ↔ Pertinence/Coût: maximizing rapid fulfillment can conflict with providing the most relevant or cost‑effective response, creating trade‑offs between speed, appropriateness and expense.

Synthesis

Fill Rate is an operational responsiveness metric: it indicates how well supply (local holdings plus processes and networks) meets demand within defined service expectations, and it requires explicit definitions of acceptable fulfillment to be interpretable.