The acceptable quality limit (AQL) is the worst-case quality level, in percentage or ratio that is still considered acceptable: in other words, it is at an acceptable quality level.

The AQL standard provides three general inspection levels, namely I, II, and III, and four special inspection levels. It determines the relationship between the lot or batch size and the sample size.

A normal inspection or general inspection level I, is used when there is no concern that the quality of the product is better or poorer than the specified quality level. A reduced inspection under a sampling plan would use the same quality level as the normal inspection but requires a smaller sample for inspection. Stricter acceptance criteria would call for the tightened inspection. The special levels are used only when relative small sample sizes are necessary and when large sampling risks may be tolerated.

The inspection level together with the lot or batch size make up the sampling size as seen in table I, where given as an example the general level II or normal inspection is preferred and the lot size is in between 3201 and 10000 pieces. The sample size is represented in the letter L.

As shown in table II, the AQL% ranges from 0.10 to 6.5. The letters Ac is the acceptance number where Re stands for the rejection number. In the given example the sample size is 200 and the agreed AQL% is 2.5. This means that if 11 or more defects are found, the shipment is rejected.