Acceptable Quality Level (AQL)

Acceptable Quality Level (AQL) is the international standard (ISO 2859-1) for statistical quality sampling during product inspections. Rather than inspecting every single unit in a production run (which would be prohibitively expensive), AQL provides a scientific method for determining how many units to randomly sample and how many defects can be found before the batch is rejected.

AQL is expressed as a percentage representing the maximum defect rate considered acceptable. The most common AQL levels used in consumer products are: AQL 0.65 for critical defects (safety hazards -- essentially zero tolerance), AQL 2.5 for major defects (functional problems that would cause a customer complaint or return), and AQL 4.0 for minor defects (cosmetic issues that most customers would not notice). These levels mean you are accepting a 0.65%, 2.5%, and 4.0% probability of defective units, respectively.

Here is how it works in practice: if your production batch is 5,000 units and you are using General Inspection Level II (the standard level), the AQL table tells you to randomly inspect 200 units. At AQL 2.5 for major defects, you can accept the batch if 10 or fewer of those 200 units have major defects, but must reject the batch if 11 or more have major defects. The sample size and accept/reject numbers are all predetermined by the AQL tables based on your batch size and chosen inspection level.