Nobody checks all 5,000 units of an order. It would take too long and cost too much. Instead, inspectors check a random sample and use statistics to decide whether the whole batch passes. That method is called AQL, and understanding it helps you set the right standard and read an inspection report properly.
The idea in one paragraph
AQL stands for Acceptance Quality Limit. It is the worst average defect rate you are willing to accept in a batch. The inspector draws a sample of a set size, counts the defects, and compares that number with a limit. At or below the limit, the batch passes. Above it, the batch fails. The sample sizes and limits come from an international standard, ISO 2859-1, so both sides are working from the same table.
Three kinds of defect
Defects are classified before the inspection, and each class gets its own limit:
- Critical: could harm the user or breaks a legal requirement. A battery that overheats, a missing safety warning. Usually zero tolerance.
- Major: the product doesn't work as intended or wouldn't be sold. A button that doesn't respond, a cracked housing.
- Minor: cosmetic, and wouldn't stop most customers buying. A small scratch, slightly uneven print.
A common setting for consumer goods is 0 for critical, 2.5 for major and 4.0 for minor defects. These are conventions, not rules; you choose the levels that fit your product and market.
A worked example
You order 5,000 wireless chargers. Under ISO 2859-1 at the standard general inspection level (Level II), a batch of that size calls for a sample of 200 units. With the common settings, the limits are:
| Defect type | AQL | Batch passes with up to | Batch fails at |
|---|---|---|---|
| Critical | 0 | 0 defects | 1 defect |
| Major | 2.5 | 10 defects | 11 defects |
| Minor | 4.0 | 14 defects | 15 defects |
If the inspector finds 1 critical defect, the batch fails, even if everything else is perfect. If they find 8 major and 12 minor defects, it passes.
What gets checked
Beyond counting defects, a final inspection usually covers:
- Quantity: is the full order produced and packed?
- Appearance and workmanship against the approved sample.
- Function: does it switch on, charge, connect?
- Measurements and weight against the specification.
- Labelling and markings: model number, CE mark, importer details, warnings.
- Packaging: retail box, inner cartons, export cartons, carton markings.
- Specific tests you agree in advance, such as a drop test or a battery check.
What AQL doesn't tell you
A pass doesn't mean the batch has no defects. With a major AQL of 2.5, you are accepting that some defective units may reach you. It also means the sample, not every unit, was checked. And a pass tells you nothing about things the inspection wasn't asked to check. The quality of the result depends on how clearly you defined your product before the inspection started.
When the batch fails
A failed inspection is information, not the end. Typical next steps: the supplier sorts and reworks the batch at its own cost, followed by a re-inspection. Agree in your contract beforehand who pays for re-inspection and what happens if a batch fails twice.
Setting it up well
- Agree the AQL levels in writing with your supplier before production.
- Provide an approved reference sample and a written specification.
- List what counts as critical, major and minor for your product.
- Schedule the final inspection when at least 80% of the goods are packed.
- Hold back your final payment until the report is in.