Every letter and its sample size
| Letter | A | B | C | D | E | F | G | H |
|---|---|---|---|---|---|---|---|---|
| Sample | 2 | 3 | 5 | 8 | 13 | 20 | 32 | 50 |
| Letter | J | K | L | M | N | P | Q | R |
|---|---|---|---|---|---|---|---|---|
| Sample | 80 | 125 | 200 | 315 | 500 | 800 | 1,250 | 2,000 |
The letter is a step between the lot and the sample. It lets one table of accept and reject numbers serve every lot size and every inspection level.
Worked example: 4,500 terracotta planters
- Table I. 4,500 planters fall in the 3,201 to 10,000 range. At general level II the letter is L.
- Table II-A. Row L means a sample of 200 planters. At AQL 2.5 the major limit is accept 10, reject 11; at AQL 4.0 the minor limit is 14 / 15.
- Check the arrows. Row L has numbers, not arrows, in both columns, so the 200 stands.
A lot of 9,000 planters would get the same letter and the same 200 pieces, because the range runs to 10,000. Sample size grows far more slowly than lot size.
When the letter is not the final sample
On small lots, the sampling table sometimes shows an arrow instead of numbers. You then follow the arrow to the next row that has a plan, and use that row's sample size. A 50-piece lot is letter D (8 pieces), but at AQL 2.5 the arrow points up to letter C: 5 pieces, accept 0, reject 1. Our Sample 03 report shows this on a 40-piece lot of dining tables.
Clear To Load reports state the code letter and the plan used for each defect class, as in the sample reports, so you can check the arithmetic. The AQL calculator follows the arrows for you.