Free tool · ANSI/ASQ Z1.4 · ISO 2859-1
AQL sampling calculator.
Enter the lot size, pick the inspection level and an AQL for each defect class, and get the sample size code letter, the sample size, and the accept and reject numbers from ANSI/ASQ Z1.4 single sampling, normal inspection, with the table’s arrow rules applied.
The tables are those of ANSI/ASQ Z1.4 (Table I and Table II-A), which match ISO 2859-1. Checked on 1 October 2026 against two published AQL calculators on 18 cases, including the arrow cases. For contract use, work from the standard your buyer names.
How the plan is read
Three steps, two tables.
AQL is the acceptance quality limit: the worst process average, in percent defective, that the plan is built to accept most of the time. It sets how many units to pull and how many defects a lot may carry.
- 1 · Code letterTable I turns the lot size and the inspection level into a code letter, A to R. General level II is the usual default; level I samples fewer units, level III more. Special levels S-1 to S-4 are for slow or destructive tests.
- 2 · Sample sizeEach code letter has a sample size, from 2 units (A) to 2,000 (R). Pull that many units at random from the whole lot, not from the top of one carton.
- 3 · Accept or rejectTable II-A gives the accept (Ac) and reject (Re) numbers for each AQL. Count the defective units by class: at or under Ac, the lot passes; at Re or over, it fails. Where the table shows an arrow, follow it, and use the new sample size.
Defects are counted per class. A cracked housing is not the same failure as a scuff, so the purchase order lists which defects are critical, major and minor, and gives each class its own AQL. The calculator works each class separately; when an arrow moves one class to a larger sample, that class is judged on its own sample.
How we use this on line watch
The plan goes in the purchase order. The count happens on the floor.
Line watch is Jack’s incoming, in-process and pre-ship checking on partner lines in Taiwan, China and Vietnam: the lot against the sample you signed, the count, the pack. A sampling plan only works when the inspector and the factory are reading the same numbers, so write the plan from this calculator into the purchase order with the defect list, and send both to Jack with your quote request.
Questions
What buyers ask about AQL.
What is AQL in product inspection?
AQL is the acceptance quality limit (often called the acceptable quality level): the worst process average, in percent defective, that a sampling plan is built to accept most of the time. It is not a promise about any one lot. With the lot size and an inspection level it fixes how many units to pull and how many defects are allowed before the lot is rejected.
What sample size do I need for 5,000 units at AQL 2.5?
At general inspection level II, a lot of 5,000 is code letter L: inspect 200 units. At AQL 2.5 the lot is accepted with 10 or fewer defects and rejected at 11. At AQL 4.0 the same 200 units accept at 14 and reject at 15.
What do the arrows in the AQL table mean?
Where Table II-A shows an arrow instead of numbers, there is no plan for that code letter at that AQL. Follow the arrow to the first row that has numbers and use that row's sample size as well as its accept and reject numbers. For example, a lot of 300 at level II is letter H (50 units), but at AQL 0.65 the arrow points down to letter J: inspect 80 units, accept on 1, reject on 2.
Why do AQL calculators give different answers?
Usually because some skip the arrow rules and keep the first sample size. For a lot of 300 at level II and AQL 0.65, Table II-A gives 80 units with accept 1 and reject 2; a calculator that ignores the arrow reports 50 units with accept 0. This calculator applies the arrows, and was checked against two published calculators that do.
Is ANSI/ASQ Z1.4 the same as ISO 2859-1?
For this purpose, yes: ANSI/ASQ Z1.4, ISO 2859-1 and the retired MIL-STD-105E use the same sample size code letters and the same single sampling plans for normal inspection. The documents differ in wording and in some supporting material. For a contract, cite the edition your buyer names.
Which AQL should I use for major and minor defects?
It is the buyer's decision, written into the purchase order with the defect list. Many consumer-goods programs use 2.5 for major defects and 4.0 for minor; stricter programs use 0.65 or 1.0 for major. Critical defects, the ones that make a product unsafe or illegal, are often set at zero accepted.
Does this cover tightened or reduced inspection?
No. It covers single sampling, normal inspection, which is where inspection normally starts. Z1.4 also defines tightened and reduced inspection and the switching rules between them; use the standard itself for those.
Cite this tool
Link to it, quote it, use it.
Free to use and to link to. If it helps your readers, the HTML below links back to it with a plain description. The tables are the standard’s; the arrows are applied.
Related
Need someone on the floor to run the plan?
Send the part, the lot size and the defect list. Jack reads inquiries himself and will tell you plainly what a line watch on your program looks like.
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