The sampling standard that lets you inspect a sample, not 100%, and still decide reliably.
The short answer
AQL (Acceptable Quality Limit) is a statistical sampling standard (ISO 2859-1 / ANSI Z1.4) that tells an inspector how many units to pull from a batch and how many defects to allow before the batch is rejected. It lets you inspect a representative sample instead of 100% of an order and still make a reliable accept-or-reject decision.
Figure 1: How AQL sampling inspection works (indicative).
Figure summary: AQL inspection draws a random sample from the lot using the AQL table for that lot size, then accepts the lot if defects are at or below the accept number and rejects it if they reach the reject number. The AQL you set (e.g. 2.5 major / 4.0 minor) defines how much defective product you will tolerate.
How AQL sampling works
From your lot size (total units) the standard gives a sample size to inspect, and for your chosen AQL level, an accept and reject number. If the sample has that many defects or fewer, the lot is accepted; more, and it is rejected. It is a way to judge a whole batch fairly from a small, statistically valid sample.
Defect classes
Critical — a defect that is unsafe or unusable; usually zero are allowed
Major — a defect likely to cause a return or complaint; a low AQL applies
Minor — a small imperfection unlikely to affect use or sale; a higher AQL is tolerated
Common AQL levels
A widely used consumer-goods setting is 0 critical / 2.5 major / 4.0 minor, meaning progressively more minor defects are tolerated than major ones and no critical defects at all. Tighten the numbers for higher-value or safety-related products, loosen them for low-cost items — the AQL should match what a defect actually costs you.
The limits of AQL
AQL is a sampling decision rule, not a guarantee that every unit is perfect. It controls the risk of accepting a bad batch, and it is only as good as the spec and golden sample the inspector judges against. Set the classes and levels before the inspection, and pair AQL with a clear specification — the number means nothing without a definition of "defect".
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It is the Acceptable Quality Limit for that defect class — roughly, the quality level at which a batch is still usually accepted. A lower AQL is stricter; 2.5 major / 4.0 minor is a common consumer-goods setting.
Does AQL mean every product is checked?
No. AQL is sampling — a statistically valid subset is inspected to decide accept or reject for the whole lot, rather than checking 100% of units.
How do I choose the right AQL?
Match it to what a defect costs you: tighter AQL (lower numbers) for high-value or safety-critical goods, looser for low-cost items. Always allow zero critical defects.