AQL sampling: understanding acceptable quality levels

Acceptable Quality Level (AQL) is a statistical method used in pre-shipment inspections to determine whether a production batch meets quality standards without inspecting every single unit.

How AQL Works

Based on the batch size, an inspection standard (typically ISO 2859-1, also known as ANSI/ASQ Z1.4) specifies how many units to sample and the maximum number of defects allowed for the batch to pass.

Key Terms

• Inspection level — General Level II is the standard default. Level I uses a smaller sample (less scrutiny), Level III a larger one (more scrutiny).
• AQL value — A percentage threshold. Common values: 1.0% for critical defects, 2.5% for major defects, 4.0% for minor defects.
• Accept/Reject numbers — The AQL table tells you: for a sample of N units, accept the batch if defects are equal to or less than X, reject if Y or more.

Example

For a batch of 5,000 units at General Level II with AQL 2.5%, you inspect 200 units. If 10 or fewer have major defects, the batch passes. If 11 or more, it fails.

Setting AQL on Faktorist

When creating a tender or purchase order, specify your required AQL levels in the quality requirements section. This ensures suppliers know your quality expectations before production begins.