AQL Sample Size Calculator
Enter your order quantity and quality limits to get the exact sample size and accept/reject numbers under ISO 2859-1 (ANSI/ASQ Z1.4) — the sampling standard used by inspectors worldwide.
Your inspection
Your sampling plan
| Defect class | AQL | Accept ≤ | Reject ≥ |
|---|
Ac = maximum defects to still pass · Re = defects that fail the lot. Based on ISO 2859-1 / ANSI Z1.4 single-sampling plans, normal inspection. How AQL works →
How to use this calculator
Enter the total number of units in your production lot, choose an inspection level, and set an AQL (Acceptable Quality Limit) for each defect class. The calculator applies the ISO 2859-1 (ANSI/ASQ Z1.4) single-sampling tables to return three things: the sample-size code letter, the number of units the inspector should pull and check at random, and the accept/reject numbers for critical, major, and minor defects.
During the inspection, the inspector counts the defects found in the sample and sorts them by class. If the number of defects in any class reaches its reject number, the lot fails that class. If every class stays at or below its accept number, the lot passes.
What AQL means
The Acceptable Quality Limit is the maximum percentage of defective units that is still considered acceptable for a given defect class. A lower AQL is stricter — it tolerates fewer defects and, all else equal, drives a larger sample and a lower accept number. Defects are graded into three classes, and each is usually assigned its own AQL:
- Critical — safety hazards or legal non-compliance. Often set to a very tight AQL, or to zero tolerance (any critical defect fails the lot).
- Major — functional faults a customer would likely return or complain about. Commonly AQL 2.5.
- Minor — cosmetic or workmanship issues that don't affect use. Commonly AQL 4.0.
The 0 / 2.5 / 4.0 combination is the most widely used default for general consumer goods, but you and your supplier should agree AQLs that match your product's risk profile.
General vs special inspection levels
The inspection level sets how large a sample you draw relative to the lot. Most visual product inspections use a General level:
- General II is the standard default and the level most inspection bookings use.
- General I draws a smaller sample (less discrimination, lower cost) — sometimes used for low-risk or trusted suppliers.
- General III draws a larger sample (more discrimination) — used for higher-risk products or tighter control.
The four Special levels (S-1 to S-4) use much smaller samples. They exist for checks where a large sample isn't practical — destructive tests, expensive or time-consuming measurements, or lab-style verification — and where a larger sampling risk is acceptable. Unless you have a specific reason to use a special level, General II is the right choice.
Where this fits in your inspection
AQL sampling is the backbone of a pre-shipment inspection, where an inspector pulls a random sample from finished, packed goods and checks it against your AQLs before you release the balance payment or ship. The same tables are used for in-process inspections and other product checks. For a full walkthrough of how the tables are built and how to read the code letters, see our AQL tables and sample size guide.
This calculator is provided for reference. Your inspection provider will confirm the exact plan on their report; if a value ever differs, follow the plan agreed in your booking.