Most buyers ask for “AQL 2.5” because someone told them to. Few read what it implies. It is worth ten minutes, because the number decides what you accept and what you can claim.
What AQL means
Acceptable Quality Limit is defined in ISO 2859-1. It sets a sampling plan: for a given lot size, a given number of units is inspected, and a maximum number of defects is allowed for the lot to pass. AQL 2.5 means the plan tolerates roughly 2.5% defective units in the batch — it does not mean 97.5% of your units are perfect.
Read the sample size first
A 1,000-piece order inspected to AQL 2.5 general level II means 80 units checked, with up to 5 major defects tolerated. On a 10,000-piece order, 200 units are checked and 10 major defects are tolerated. The tolerance scales with the lot, which is why large orders need a tighter AQL or a 100% check.
| Lot size | Sample size | Critical | Major (AQL 2.5) | Minor (AQL 4.0) | |
|---|---|---|---|---|---|
| 151–280 | 32 | 1 | 2 | 3 | 5 |
| 281–500 | 50 | 1 | 2 | 5 | 7 |
| 501–1,200 | 80 | 2 | 3 | 5 | 10 |
| 1,201–3,200 | 125 | 3 | 5 | 7 | 14 |
| 3,201–10,000 | 200 | 5 | 7 | 10 | 21 |
Critical, major, minor
A critical defect is one that could injure a user or make the product illegal — a live conductor exposed, a choking hazard on a children’s item. Critical defects fail the lot at any AQL. Major defects affect function or saleability. Minor defects affect appearance only.
Good inspection reports classify the defect you found, photograph it with the carton number, and state the AQL result explicitly rather than describing the goods as “acceptable”.
When AQL 2.5 is the wrong choice
Three situations call for more: regulated categories (toys, electricals, food contact, children’s products) where a single failure can trigger a recall; high-value low-volume goods where the cost of a return exceeds the cost of full inspection; and any order where the defect is invisible in a sample — sealed bottles that leak, electronics that fail after thermal cycling.
In those cases we run AQL 1.5 or 0.65 and add a 100% function test on the characteristic that matters.
What the report cannot tell you
It cannot tell you how the goods will behave after three months in a warehouse, and it cannot catch a defect that only appears in use. Sampling is a risk-reduction tool, not a warranty. The warranty is the contract, the balance you withhold, and the factory relationship you maintain.
AQL 2.5 does not mean 97.5% perfect. It means you accepted a sampling plan that tolerates 2.5% defects.
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