How AQL inspection works, from sample size to final payment.

AQL stands for acceptance quality limit. ISO 2859-1 sets out sampling schemes indexed by AQL for lot-by-lot inspection by attributes: each piece in the sample is judged conforming or not, and the defects are counted. Its third edition, published in January 2026, replaced the 1999 edition. Inspection companies cite it together with its American counterpart, ANSI/ASQ Z1.4.

The AQL is not a promise about the whole lot. The NIST handbook of engineering statistics describes it as the baseline quality level that a sampling plan is designed to accept with a high probability. A lot slightly worse than the AQL can still pass, and a good lot can occasionally fail: that is the price of checking a sample instead of every piece.

The standard is designed for a series of lots from the same supplier. It switches to tightened inspection when quality deteriorates and allows reduced inspection when quality stays good.

Two inputs set the sample size: the lot size and the inspection level. There are three general levels (I, II and III) and four special levels (S-1 to S-4). Level II is the default for general consumer goods. Level I checks fewer pieces and level III more; the special levels are for cases where small samples are necessary and a larger sampling risk is acceptable.

The lot size and the level give a code letter. The code letter gives the sample size and, for each AQL, an acceptance number and a rejection number. If the sample contains no more defects than the acceptance number, that class passes; at the rejection number or above, the lot fails.

For the same 5,000 units, level I samples 80 pieces and level III 315. A larger sample takes more inspection time and gives a sharper answer.

Defects are sorted into classes before the inspection, and each class gets its own AQL.

• +Critical: a safety or compliance failure, a product that could hurt the user or break the rules of the destination market.
• +Major: a defect that affects function or appearance enough that the customer would likely return the product.
• +Minor: a small cosmetic defect that does not affect function.

These values are common practice among inspection companies, not a requirement of the standard. The buyer chooses them and writes them into the order, together with a defect list that says which defect belongs to which class.

1. 01

   Pre-production check

   At the start of production, also called an initial production check: raw materials, components and the production setup, before the full quantity is made.

2. 02

   During production

   While the lines are running: defects, delays and process problems found while they can still be corrected.

3. 03

   Pre-shipment inspection

   When production is complete and at least 80% of the goods are packed, so the sample comes from the finished lot. This is the AQL inspection most buyers link to the balance.

4. 04

   Container loading check

   At loading: products, quantities, packaging condition and carton marks, the cleanliness of the container and the way the goods are stowed.

A first order with a new supplier, or a product with safety-critical features, justifies more than one stage. A repeat order from a supplier with a clean record may need only the pre-shipment inspection.

• +The order reference, the quantity found against the quantity ordered, and the sampling plan applied: lot size, level, sample size and AQL per class.
• +Packaging, labelling and shipping marks, barcodes included, checked against your instructions.
• +Workmanship and appearance, with every defect counted, classified critical, major or minor, and photographed.
• +Function tests, measurements and on-site tests such as carton drop tests, as the checklist requires.
• +A result for each checkpoint and an overall pass or fail against the agreed AQL.

A report is only as good as its reference. Give the inspector the approved sample, the specifications and the defect list before the visit.

An inspection protects you only while money still depends on it. A common structure is a deposit before production and the balance once the goods are ready; the safer version makes the balance due after the pre-shipment inspection. A pass then gives you documented evidence of quality before you pay, and a fail gives you independent evidence to demand corrections before you settle.

• +The plan: ISO 2859-1, general inspection level II, and the AQL for each defect class.
• +The reference: approved sample, specifications, packaging instructions and defect list.
• +The trigger: the balance is due within a set number of days after a report with an overall pass.
• +The failure path: sorting or rework by the supplier, then a new inspection, with who pays for it stated in advance.
• +Access: the inspector picks the cartons at random, and the factory provides space, tools and staff to open them.