AQL inspection: how to read the table, inspection levels and acceptance numbers

THURSDAY, 12 NOVEMBER 2026

From lot size to code letter, from sample size to acceptance and rejection numbers: how to use ISO 2859-1 as updated in 2026, which AQLs to choose for critical, major and minor defects, and an example on 5,000 umbrellas.

AQL inspection is the sampling method that tells you how many pieces to check in a lot of goods and how many defects the sample may contain before the whole shipment is rejected. The table is read in two steps: the lot size gives a code letter, and the letter gives the number of pieces to inspect and the acceptance and rejection numbers.

For anyone importing consumer goods, promotional items or components from Asia, it is the common language of pre-shipment checks: supplier, inspector and importer agree on a string such as "AQL 2.5 / 4.0, level II" and the sample, the thresholds and the result all follow from it. This guide explains what AQL means, which standard governs it, how to read the table step by step, which values to choose, what the table does not guarantee and a worked example with numbers.

AQL inspection: what AQL means

AQL stands for acceptance quality limit, and it is also found as acceptable quality level. It is the worst average defect level, expressed as a percentage, that the buyer still considers tolerable for a supplier's production. It is not the number of defective pieces allowed in the lot: it is a parameter that selects a sampling plan.

Sampling by attributes works like this: instead of checking every piece, a sample is drawn at random, the defective pieces are counted and the total is compared with two thresholds. If the defectives are equal to or below the acceptance number (Ac), the lot passes; if they reach the rejection number (Re), the lot is rejected. The check usually takes place during the pre-shipment inspection, when production is finished and the goods are still at the factory.

The reference standard: ISO 2859-1, updated in 2026

AQL tables come from ISO 2859-1, "Sampling procedures for inspection by attributes, Part 1: Sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection". The current edition is ISO 2859-1:2026, published in January 2026, which replaces the 1999 edition, the 2001 corrigendum and the 2011 amendment.

The standard defines single, double and multiple sampling plans; consumer goods inspections almost always use the single sampling plan for normal inspection, the one described in this guide. Its stated aim is to push the producer to keep the process average at least at the agreed AQL, through the economic risk of having a lot rejected, and to put a limit on the buyer's risk of accepting a poor lot. In the United States the equivalent standard ANSI/ASQ Z1.4, 2008 edition, is used, and many inspection companies build their tables on it: in the most common plans the values are the same.

Step one: from lot size to code letter

The first table crosses the lot size with the inspection level and returns a code letter. The lot is the set of pieces of the same item made under the same conditions and presented together for inspection, for example all 5,000 umbrellas in an order.

With general level II, the one used when the contract says nothing else, the most frequent bands in orders of promotional items and consumer goods are these: from 501 to 1,200 pieces letter J, from 1,201 to 3,200 letter K, from 3,201 to 10,000 letter L, from 10,001 to 35,000 letter M, from 35,001 to 150,000 letter N. The letter does not yet say how many pieces to check: it only leads into the second table.

Step two: sample size and acceptance numbers

The second table, the single sampling plans for normal inspection, gives each letter a sample size and, for each AQL value, the Ac and Re pair. These are the values for the most used letters and for the two most common AQLs in consumer goods:

• letter J, sample of 80 pieces: at AQL 2.5 accept up to 5 defectives and reject from 6; at AQL 4.0 accept up to 7 and reject from 8;
• letter K, sample of 125 pieces: at AQL 2.5 accept up to 7 and reject from 8; at AQL 4.0 accept up to 10 and reject from 11;
• letter L, sample of 200 pieces: at AQL 2.5 accept up to 10 and reject from 11; at AQL 4.0 accept up to 14 and reject from 15;
• letter M, sample of 315 pieces: at AQL 2.5 accept up to 14 and reject from 15; at AQL 4.0 accept up to 21 and reject from 22.

The table also contains arrows: they mean that there is no plan of its own for that combination of letter and AQL and that the first plan above or below the arrow must be used, with its sample size. If the sample shown is equal to or larger than the lot, 100% of the pieces are inspected. Arrows matter mostly in small lots and with very low AQLs.

Critical, major and minor defects: which AQL to choose

Defects fall into three classes and each has its own AQL. Critical defects make the product unsafe or non-compliant with mandatory rules, for example a sharp edge or a missing CE marking; major defects can cause a failure or reduce usability or saleability, such as a zip that does not close or an illegible print; minor defects are workmanship flaws that do not affect use, such as a loose thread or a barely visible scratch.

The usual practice in consumer goods inspections is: 0 for critical defects, meaning no critical piece allowed in the sample; 2.5 for major defects; 4.0 for minor defects. For higher-value or higher-risk products the major AQL drops to 1.0 or 1.5 and the minor one to 2.5. The three classes are counted separately: a lot can exceed the minor defect threshold and be rejected even if the major one is respected.

Inspection levels: I, II, III and special

The inspection level sets how large the sample is compared with the lot. The standard provides three general levels and four special ones. Level II is the normal one and applies unless something else is specified. Level I reduces the sample and is used with suppliers that have regularly passed previous inspections; level III increases it and is used with suppliers that have had recent problems or with high-value goods.

For a lot of 5,000 pieces the sample is 80 pieces at level I, 200 at level II and 315 at level III. Special levels, from S-1 to S-4, produce very small samples and are used for destructive or lengthy tests, such as a drop or seal test, where checking 200 pieces would make no sense. In repeated inspections the standard also provides rules to switch from normal to tightened or reduced inspection based on the results of previous lots.

What the AQL table does not guarantee

A lot that passes inspection at AQL 2.5 does not necessarily contain at most 2.5% defective pieces. In the letter L plan up to 10 defectives out of 200 are accepted, that is 5% of the sample, and the sample is still an estimate: the rest of the lot may contain more or fewer. AQL is a statistical parameter that balances the supplier's risk of having a good lot rejected and the buyer's risk of accepting a poor one, not a guarantee on each piece.

This points to two practical precautions. The sample must be drawn truly at random, from different cartons and not from those prepared by the supplier. And critical defects, those linked to safety, should also be covered by laboratory tests and compliance documents: a visual inspection on a sample does not replace the tests required by product rules.

A worked example: 5,000 custom umbrellas

The example is hypothetical. A company orders 5,000 folding umbrellas with a printed logo in China and sets in the contract a pre-shipment inspection at "AQL 0 / 2.5 / 4.0, general level II". The lot falls in the band from 3,201 to 10,000 pieces, so letter L and a sample of 200 umbrellas, drawn at random from the cartons.

The inspector finds 0 critical defects, 8 major defects (bent ribs, crooked logo) and 16 minor defects (loose threads, small marks). Major defects stay below the acceptance number of 10, but minor ones exceed the rejection number of 15: the lot is rejected. The supplier must sort and rework the pieces, then the inspection is repeated on the same plan. Had the contract set level III, the sample would have been 315 umbrellas, accepting up to 14 major and 21 minor defects; with level I only 80, accepting up to 5 major and 7 minor.

AQL inspection in short: the checklist

Before confirming an order it is worth writing these points into the contract:

• the three AQL values for critical, major and minor defects, for example 0 / 2.5 / 4.0;
• the inspection level, usually general level II, and the reference standard, ISO 2859-1;
• the list of defects with the class of each, prepared on the approved sample;
• the tests to run at the factory during the inspection, such as function, drop or measurement checks;
• what happens if the lot is rejected: sorting, rework, re-inspection and who pays for it.

With La Merce, an order of 5,000 umbrellas or gadgets from China starts with the AQL plan already written into the contract and the defect list classified on the approved sample, so the inspector knows that out of 200 pieces the fifteenth minor defect gets the lot rejected.

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