AQL ChartWhat AQL 2.5 means, with the numbers from the table
AQL 2.5 is one of the 26 AQL columns in the sampling table. On its own it does not tell you how many units to inspect or how many defective units you may find. Those come from the row, and the row comes from your lot size and inspection level.
AQL 2.5 at general inspection level II
This is the 2.5 column of Table II-A of MIL-STD-105E, for single sampling under normal inspection, with the code letter that Table I gives for each lot size at level II.
| Lot size | Code letter | Cell at AQL 2.5 | Sample size used | Ac | Re |
|---|---|---|---|---|---|
| 2 to 8 | A | down arrow, to C | 5 | 0 | 1 |
| 9 to 15 | B | down arrow, to C | 5 | 0 | 1 |
| 16 to 25 | C | 0 1 | 5 | 0 | 1 |
| 26 to 50 | D | up arrow, to C | 5 | 0 | 1 |
| 51 to 90 | E | down arrow, to F | 20 | 1 | 2 |
| 91 to 150 | F | 1 2 | 20 | 1 | 2 |
| 151 to 280 | G | 2 3 | 32 | 2 | 3 |
| 281 to 500 | H | 3 4 | 50 | 3 | 4 |
| 501 to 1,200 | J | 5 6 | 80 | 5 | 6 |
| 1,201 to 3,200 | K | 7 8 | 125 | 7 | 8 |
| 3,201 to 10,000 | L | 10 11 | 200 | 10 | 11 |
| 10,001 to 35,000 | M | 14 15 | 315 | 14 | 15 |
| 35,001 to 150,000 | N | 21 22 | 500 | 21 | 22 |
| 150,001 to 500,000 | P | up arrow, to N | 500 | 21 | 22 |
| 500,001 and over | Q | up arrow, to N | 500 | 21 | 22 |
Ac is the acceptance number and Re the rejection number. For a lot of 5,000 units: inspect 200. With 10 or fewer defective units the lot is accepted; with 11 or more it is rejected (clause 4.10.1.1).
Where the sample size equals or exceeds the lot, the footnote to the table calls for 100 percent inspection. In the first row that applies to lots of 5 units or fewer.
Three things the table shows
The sample does not grow in step with the lot. A lot of 500 is sampled with 50 units. A lot of 100,000 is sampled with 500.
For the largest lots the sample stops growing. At AQL 2.5 the cells for letters P and Q are up arrows, and both lead back to letter N. From 35,001 units upward the plan is the same: 500 units, Ac 21, Re 22.
For small lots the acceptance number is zero. Up to 50 units the plan is 5 units with Ac 0 and Re 1: a single defective unit in the sample rejects the lot.
What the 2.5 stands for
Clause 3.1 of MIL-STD-105E defines the AQL as the quality level which, for the purposes of sampling inspection, is the limit of a satisfactory process average, when a continuous series of lots is considered. Its note says the AQL is a designated value of percent defective (or defects per hundred units) for which lots will be accepted most of the time by the sampling procedure being used.
So 2.5 describes a supplier's long-run average: if the average stays at or below 2.5 percent defective, the great majority of lots will pass.
What it does not stand for
- Not a cap on the sample. At letter L the lot passes with 10 defective units in 200, which is 5 percent of the sample.
- Not a statement about one lot. The note to clause 3.1 says the AQL alone does not identify the chances of accepting or rejecting individual lots, and that the probability of acceptance at the AQL depends on the sample size. The risks for a given plan are read from its operating characteristic curve.
- Not permission to ship defects. Clause 4.4.2: the selection or use of an AQL shall not imply that the contractor has the right to supply any defective unit of product.
At other inspection levels
The inspection level changes the code letter, and with it the row. For a lot of 5,000 units at AQL 2.5:
| Inspection level | Code letter | Sample size | Ac | Re |
|---|---|---|---|---|
| I | J | 80 | 5 | 6 |
| II | L | 200 | 10 | 11 |
| III | M | 315 | 14 | 15 |
Use the calculator for any other lot size, level or AQL, or read the full single sampling table.
Questions people ask
How many defects are allowed at AQL 2.5?
It depends on the row. At general level II the acceptance number runs from 0 for the smallest lots to 21 for lots above 35,000 units, as the table above shows.
Is AQL 2.5 a percentage of the sample?
No. The acceptance number comes from the table, not from multiplying the sample size by 2.5 percent. For a sample of 200 the acceptance number at AQL 2.5 is 10.
Can AQL 2.5 be read as defects per hundred units?
Yes. Clause 4.4.3 says AQL values of 10.0 or less may be expressed either in percent defective or in defects per hundred units.
Source
- MIL-STD-105E, Sampling Procedures and Tables for Inspection by Attributes, U.S. Department of Defense, 10 May 1989: Table I, Table II-A with its footnote, and clauses 3.1, 4.4.2, 4.4.3 and 4.10.1.1. Page scans: archive.org/details/MIL-STD-105E_1. Read 11 October 2026.
Where your contract names ANSI/ASQ Z1.4, ISO 2859-1 or another standard, use the tables of that edition.