AQL quality control explained for workwear buyers

What AQL is

AQL stands for Acceptance Quality Limit, often called acceptable quality level. It is the level of defects, expressed as a percentage, that the buyer considers acceptable on average for a production run.

The international reference is ISO 2859 Part 1, "Sampling procedures for inspection by attributes". It sets out sampling schemes indexed by AQL for lot by lot inspection. The third edition was published in January 2026 and replaces the 1999 edition and its amendments. According to ISO, it applies among other things to finished products and to series of lots from a single process or supplier.

The principle is simple:

• a sample is drawn at random from the lot;
• the defects found are counted;
• if that number does not exceed the acceptance number in the table, the lot is accepted; if it reaches the rejection number, the lot is rejected.

An AQL therefore does not promise that every lot contains fewer defects than the stated percentage. It sets a decision rule based on a sample.

How the sample size is determined

Sample size depends on two things: the lot size and the chosen inspection level. The tables in the standard first give a code letter, then the sample size and the acceptance and rejection numbers for each AQL value.

Example: for a lot of 1,201 to 3,200 pieces at general level II, the code letter is K and the sample is 125 pieces.

Inspection levels

The standard has two families of levels.

• General levels I, II and III. Level II is the default. Level I checks fewer pieces, level III more. According to the consultancy Sofeast, for an order of 5,000 pieces the sample ranges from 80 pieces at level I to 315 pieces at level III.
• Special levels S1 to S4. They are used when a small sample is needed and a higher sampling risk can be accepted, for example for destructive or time consuming tests.

The standard also provides for normal, tightened and reduced inspection. Inspection usually starts at normal, then moves to tightened if several recent lots were rejected, or to reduced after a run of accepted lots.

Critical, major and minor defects

A single lot is often judged against three different AQLs, one for each defect severity.

• Critical defect: a defect that could make the product unsafe for the user or that breaches regulations. The AQL is usually set at 0: a single critical defect in the sample is enough to reject the lot.
• Major defect: a defect that reduces the usability of the garment or that is clearly visible and would affect its sale, for example a seam that comes open or a misplaced pocket.
• Minor defect: a small deviation that does not affect use, for example an untrimmed thread.

According to guides published by inspection companies, a combination often seen for consumer goods is 0 for critical defects, 2.5 for major and 4.0 for minor. This is not a requirement of the standard: the buyer decides.

How to choose your level

A few questions help you set the level that suits you.

• What is the garment used for? Protective or high visibility clothing calls for a precise list of critical defects.
• What is your experience with the supplier? According to Sofeast, level III makes sense after recent quality problems, and level I when most previous inspections were passed.
• What counts as a defect? An AQL only means something with a written defect list, classified by severity, and measurement tolerances in the tech pack.
• Who inspects? The factory, your own team or an independent inspection company. All three can work with the same tables.

The simplest approach is to write these choices into the order: inspection level, AQL per severity, defect list and tolerances.

During production inspection and final inspection

AQL applies at several points.

• During production inspection. According to QIMA, it takes place when 20 to 80% of production is complete. It checks finished and semi finished pieces, specifications (colours, construction, labels, measurements) and packing. Its value is that a defect can be corrected before the whole lot is made.
• Final inspection before shipment. Again according to QIMA, it is carried out when 80 to 100% of production is complete. This is usually the inspection used to accept or reject the lot.

Before both stages, the client's approval of the prototype sets the reference against which production is compared.

At Vestra

At Vestra, quality control follows 5 checkpoints: incoming materials, inline checks on the production line, end of line inspection, measurement check and inspection at packing. The AQL level is set by the client for each order. The prototype is approved by the client before production, and the client follows the inspection stage of each order on the online client portal. Visits to the factory in Sidi Bou Ali, near Sousse, are possible by appointment.

To discuss your project, send your tech pack to sales@vestratextile.com.

FAQ

Does AQL 2.5 mean that 2.5% defective pieces are accepted?

Not exactly. The AQL is used to read the sampling table. It is the number of defects found in the sample, compared with the acceptance and rejection numbers, that decides the outcome for the lot.

Is level II mandatory?

No. It is the default level, but the buyer can choose another general level or a special level depending on the need.

Can there be a different AQL for each type of defect?

Yes. That is actually common practice: one AQL for critical defects, one for major and one for minor.

Vestra Manufacturing, workwear manufacturer in Tunisia →

Sources

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