AQL ChartAQL inspection levels: code letters for General I, II, III and Special S-1 to S-4
Find your lot size in the left column of Table 1, read across to your inspection level, and the cell gives the code letter. Table 2 then gives the sample size for that letter. Once an AQL is applied, an arrow in Table II-A can move you to a different letter, and a different sample size with it.
If you are not yet sure which level applies to your shipment, the article how to choose an inspection level covers that separately.
Table 1: code letter by lot size and inspection level
| Lot size | S-1 | S-2 | S-3 | S-4 | I | II | III |
|---|---|---|---|---|---|---|---|
| 2 to 8 | A | A | A | A | A | A | B |
| 9 to 15 | A | A | A | A | A | B | C |
| 16 to 25 | A | A | B | B | B | C | D |
| 26 to 50 | A | B | B | C | C | D | E |
| 51 to 90 | B | B | C | C | C | E | F |
| 91 to 150 | B | B | C | D | D | F | G |
| 151 to 280 | B | C | D | E | E | G | H |
| 281 to 500 | B | C | D | E | F | H | J |
| 501 to 1,200 | C | C | E | F | G | J | K |
| 1,201 to 3,200 | C | D | E | G | H | K | L |
| 3,201 to 10,000 | C | D | F | G | J | L | M |
| 10,001 to 35,000 | C | D | F | H | K | M | N |
| 35,001 to 150,000 | D | E | G | J | L | N | P |
| 150,001 to 500,000 | D | E | G | J | M | P | Q |
| 500,001 and over | D | E | H | K | N | Q | R |
Table 2: sample size by code letter
| Code letter | Sample size |
|---|---|
| A | 2 |
| B | 3 |
| C | 5 |
| D | 8 |
| E | 13 |
| F | 20 |
| G | 32 |
| H | 50 |
| J | 80 |
| K | 125 |
| L | 200 |
| M | 315 |
| N | 500 |
| P | 800 |
| Q | 1250 |
| R | 2000 |
There is no letter I or O in Table 2.
What the letter does not tell you yet
The sample size in Table 2 is the one that belongs to the letter on its own. In Table II-A, which is the table for normal inspection, a letter sits next to an arrow once an AQL is applied, and the legend tells you to use the first sampling plan below the arrow, or above it. So the plan you actually run can belong to another letter.
One example, at AQL 2.5: a lot of 51 to 90 at level II gives letter E in Table 1, and letter E carries sample size 13 in Table 2. At AQL 2.5 the plan used is letter F's, sample size 20, accept 1, reject 2.
The same lot range of 51 to 90 at AQL 2.5 gives two other results. At level I the letter is C, so sample size 5, accept 0, reject 1. At level III the letter is F, so sample size 20, accept 1, reject 2.
If the sample size equals or exceeds the lot or batch size, do 100 percent inspection.
Where these tables 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.
Questions people ask
Which code letter does a lot of 51 to 90 get at level II?
Letter E.
What sample size belongs to letter E?
13.
What is the smallest sample size in Table 2?
2, for letter A.
Source
- 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 any standards body, and where your contract names ANSI/ASQ Z1.4, ISO 2859-1 or another standard, use the tables of that edition.