Common mistakes when reading an AQL table

Parts of this article describe common industry practice, not official rules; statements taken from official pages are listed under Sources.

The AQL table is easy to misread at some points. These slips are: using the sample size of the row's own code letter after an arrow moves the plan to another letter; reading the wrong inspection level column; placing a lot on the wrong row at a range boundary; mixing up Ac and Re; treating the AQL as the share of the sample that may be defective; overlooking the footnote for small lots; and using this table when the contract names tightened or reduced inspection or another standard or edition.

The step-by-step reading is on How to read an AQL table.

Where readers usually slip

Using the sample size of the row's own code letter

A lot at inspection level II is assigned a code letter. A reader may take the sample size that belongs to that letter and use it for every acceptance quality limit. But for some AQLs the table sends the plan to another letter through an arrow. Reading the original letter's sample size there gives the wrong plan.

What the table shows: at level II, a lot of 91 to 150 is code letter F, and the sample size of that letter is 20. At AQL 1.0 the plan used is letter E's: sample size 13, accept 0, reject 1. At AQL 1.5 the plan used is letter G's: sample size 32, accept 1, reject 2. At AQL 2.5 the plan is F's own: sample size 20, accept 1, reject 2.

Reading the wrong inspection level column

The table lists inspection levels. A reader may read the sample size from the wrong level column for the same lot and AQL, and end up with a plan the contract did not intend.

What the table shows: a lot of 5,000 falls in the range 3,201 to 10,000. At AQL 2.5, level I gives code letter J, sample size 80, accept 5, reject 6. Level II gives code letter L, sample size 200, accept 10, reject 11. Level III gives code letter M, sample size 315, accept 14, reject 15.

Placing a lot on the wrong row at a range boundary

Lot size ranges meet at boundaries. A reader may put a lot on the row for the next range, or the previous one, and pick the wrong code letter.

What the table shows: at level II and AQL 2.5, the range 1,201 to 3,200 is code letter K, sample size 125, accept 7, reject 8. The range 3,201 to 10,000 is code letter L, sample size 200, accept 10, reject 11. A lot of exactly 3,200 belongs to the first range; a lot of 3,201 belongs to the second.

Mixing up Ac and Re

The acceptance number (Ac) and the rejection number (Re) sit next to each other. A reader may treat Re as the number allowed, or read Ac as the point to reject. The two mean opposite things.

What the table shows: the reading rule on this page is, inspect the sample; if the number of defective units is Ac or fewer, the lot is accepted, and if it is Re or more, the lot is rejected. For the level II plan at a lot of 5,000, code letter L, the plan is sample size 200, accept 10, reject 11.

Treating the AQL as the share of the sample that may be defective

A reader may think the AQL is a percentage of the sample that can be defective, and try to work out the acceptance number from it. The AQL is not a percentage of the sample.

What the table shows: the acceptance number is read from the table cell for the code letter and the AQL; it is not worked out from the AQL. For code letter L at AQL 2.5, the table gives a sample size of 200, accept 10, reject 11.

Overlooking the footnote for small lots

For very small lots the sample size after the arrow can be close to or larger than the lot. A reader may miss the footnote that changes the instruction when that happens.

What the table shows: a lot of 2 to 8 at level II and AQL 2.5 uses code letter A, and following the arrow gives a sample size of 5, accept 0, reject 1. The Table II-A footnote says that if the sample size equals or exceeds the lot or batch size, do 100 percent inspection.

Using this table when the contract names another inspection type or standard

A reader may apply this table even when the contract calls for a different inspection type or a different standard. The plan in force is the one the contract names.

What the table shows: this table covers single sampling under normal inspection only. Where a contract or purchase order names a standard and an edition, that one governs.

Where the table values come from

These tables come from MIL-STD-105E, Sampling Procedures and Tables for Inspection by Attributes (U.S. Department of Defense, 10 May 1989). ANSI/ASQ Z1.4 and ISO 2859-1 descend from it. The tables here were not compared cell by cell with the current paid editions of ANSI/ASQ Z1.4 or ISO 2859-1. Where a contract or purchase order names a standard and an edition, that one governs.

FAQ

Can I use this table for tightened or reduced inspection?

This table covers single sampling under normal inspection only. Your contract or purchase order may name tightened inspection, reduced inspection, or a different standard and edition. In that case, the standard and edition named in the contract govern.

What is the difference between Ac and Re?

Ac is the acceptance number and Re is the rejection number. Inspect the sample; if the number of defective units is Ac or fewer, the lot is accepted, and if it is Re or more, the lot is rejected.

Sources

• MIL-STD-105E, Sampling Procedures and Tables for Inspection by Attributes, U.S. Department of Defense, 10 May 1989: Table I and Table II-A with its legend and footnote. Page scans: archive.org/details/MIL-STD-105E_1. Read 11 October 2026.

Checked 11 October 2026.

This page is an unofficial reference, not affiliated with ISO, ASQ or ANSI, and where your contract names ANSI/ASQ Z1.4, ISO 2859-1 or another standard, use the tables of that edition.