QM Bench

AQL Sampling Plan Calculator (ISO 2859-1 / ANSI Z1.4)

Enter the lot size, inspection level and AQL to get the sample size and the accept and reject numbers for single sampling, normal inspection, with the operating characteristic curve.How to use ↓
  1. 1Enter your data
  2. 2Read the verdict
  3. 3Download the PDF report

Sample 80, accept on 2, reject on 3

Take 80 units at random from the lot of 1000. Accept if 2 or fewer are nonconforming, reject if 3 or more.

Code letter JLevel IIAQL 1 %Normal inspection
Sample size n
80
Accept on (Ac)
2
Reject on (Re)
3
LTPD (Pa 10 %)
6.52
% defective rejected 90 % of the time

Operating characteristic (OC) curve

probability of accepting a lot with a given % defective
0%20%40%60%80%100%0.0%1.0%2.0%3.0%4.0%5.0%6.0%7.0%8.0%9.0%10.0%95 % at 1.0 %10 % at 6.5 %Lot fraction defectiveProbability of acceptance

Lots with 1.0 % defective are accepted 95 % of the time (producer's risk 5 %). Lots with 6.5 % defective are still accepted 10 % of the time (consumer's risk).

Sample size code letters

ISO 2859-1 Table 1
Lot sizeS-1S-2S-3S-4IIIIII
2 – 8AAAAAAB
9 – 15AAAAABC
16 – 25AABBBCD
26 – 50ABBCCDE
51 – 90BBCCCEF
91 – 150BBCDDFG
151 – 280BCDEEGH
281 – 500BCDEFHJ
501 – 1,200CCEFGJK
1,201 – 3,200CDEGHKL
3,201 – 10,000CDFGJLM
10,001 – 35,000CDFHKMN
35,001 – 150,000DEGJLNP
150,001 – 500,000DEGJMPQ
500,001 and overDEHKNQR

Sample sizes: 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

Single sampling, normal inspection, without switching rules. Check the plan against your copy of the standard before using it in a contract.

How it works

  1. The lot size and inspection level give the sample size code letter (ISO 2859-1 Table 1).
  2. The code letter and AQL give the sample size and Ac / Re in the master table (Table 2-A, normal inspection).
  3. The OC curve shows how likely a lot with a given percent defective is to be accepted.

The plans are checked against reference values from ISO 2859-1, see the validation report. Switching rules to tightened or reduced inspection are not included. To decide how many parts you need for other purposes, use the sample size calculator.

Frequently asked questions

›What does AQL mean?

Acceptable quality limit: the worst process average (percent nonconforming) that is still considered acceptable for sampling inspection. An AQL of 1.0 does not mean 1 % defects are acceptable in your product, it is a parameter of the sampling plan.

›Which inspection level should I use?

General inspection level II is the default. Level I uses smaller samples, level III larger ones. Special levels S-1 to S-4 are for destructive or expensive tests where small samples are needed.

›What do Ac and Re mean?

Ac is the acceptance number: accept the lot if the number of nonconforming units in the sample is at most Ac. Re is the rejection number: reject if it is Re or more.

›What do the arrows in the AQL table mean?

Some combinations of code letter and AQL have no plan in the table, only an arrow. You then use the first plan below or above the arrow, with its sample size. The tool follows the arrows automatically and tells you when it did.

›Is AQL sampling acceptable in automotive?

Many automotive customers require zero defects and do not accept AQL plans with acceptance numbers above 0. Use AQL sampling for incoming inspection where agreed, and statistical process control for your own processes.