AQL Sampling Calculator (ISO 2859-1 / ANSI/ASQ Z1.4)
Find the AQL sample size, code letter and accept/reject numbers for any lot size, inspection level and AQL, for major and minor defects — single sampling, normal inspection (ISO 2859-1, ANSI/ASQ Z1.4).
How it works
Lot size + inspection level → sample size code letter (Table 1) · code letter + AQL → sample size n, acceptance number Ac and rejection number Re (Table 2-A, single sampling, normal inspection; follow the arrow to the first plan above or below when the cell has none) · Accept the lot if defects found ≤ Ac, reject if ≥ Re.
AQL (acceptance quality limit) sampling is the lot-by-lot inspection scheme of ISO 2859-1, which is technically equivalent to ANSI/ASQ Z1.4 and the former MIL-STD-105E. General level II is the default for most consumer-goods inspections; level I takes smaller samples and level III larger ones, while the special levels S-1 to S-4 are for costly or destructive tests. Importers usually set AQL 0 for critical, 2.5 for major and 4.0 for minor defects. When the table points to a sample size larger than the lot, the whole lot is inspected.
Worked example
A lot of 1,000 units at general inspection level II falls in the 501–1,200 range, so the code letter is J and the sample size is 80 units. For major defects at AQL 2.5 the lot is accepted with 5 or fewer defects and rejected at 6; for minor defects at AQL 4.0 the same 80 units are accepted with up to 7 and rejected at 8. You inspect 8.00% of the lot.
Sources: ISO 2859-1 Sampling procedures for inspection by attributes · ASQ — ANSI/ASQ Z1.4 sampling procedures and tables for inspection by attributes
Frequently asked questions
What does AQL 2.5 mean?
It is the worst process average, in percent defective, that is still considered acceptable over many lots — not a limit on one lot. A supplier running at or below 2.5% defective will have the large majority of its lots accepted.
What sample size do I need for a lot of 1,000 pieces?
At general inspection level II the code letter is J, so you inspect 80 pieces. At level I the letter is G (32 pieces) and at level III it is K (125 pieces).
Why does the sample size change for some AQL values?
Some cells in the master table contain an arrow instead of a plan. You follow the arrow to the first plan above or below it, which can use a different code letter and sample size. If the major and minor plans end up with different sample sizes, inspect the larger sample and apply each plan to its own part.
What AQL is used for critical defects?
Critical defects (those that make the product unsafe or illegal) are normally set at AQL 0: a single critical defect in the sample rejects the lot.
Is ANSI Z1.4 the same as ISO 2859-1?
For single sampling the code letters, sample sizes and accept/reject numbers are the same. The standards differ in some switching rules and wording, so cite the one your contract specifies.
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This calculator is for educational purposes. Double-check important results before acting on them.