AQL sample size calculator
Enter the number of units in your order and the AQL for each type of defect. The calculator uses the ISO 2859-1 (ANSI/ASQ Z1.4) single sampling tables for normal inspection to give the sample size and the number of defects at which the order passes or fails.
Updated
Lot of 3,000 units at inspection level II gives sample size code letter K.
The lot passes for a defect class if the defects found in the sample are at or below the accept number, and fails at the reject number. Each class is judged on its own sample size and limits. Where they differ, many inspectors simply check the largest sample, which covers the others.
How AQL sampling works
- 1Find the sample size code letter from the lot size and the inspection level. General Inspection Level II is the usual default.
- 2Use the code letter and the AQL to find the sampling plan: how many units to inspect, the accept number and the reject number.
- 3Inspect the sample. If the defects found are at or below the accept number, the lot passes. At the reject number, it fails.
Some combinations point to a different code letter in the table (shown as arrows in the standard). The calculator follows those arrows for you, which is why the sample size can change when you change the AQL.
Which AQL to choose
| Defect type | What it means | Common AQL |
|---|---|---|
| Critical | Unsafe, or breaks the law in your market | Not allowed (0) |
| Major | Likely to cause a return or complaint | 2.5 (1.0 or 1.5 for high-value goods) |
| Minor | Small difference most customers would accept | 4.0 |
Inspection levels
- Level II is the normal level and the default for most pre-shipment inspections.
- Level I uses smaller samples, for low-risk goods or a supplier with a good record.
- Level III uses larger samples, for high-risk goods or a supplier you don't trust yet.
- Special levels S1 to S4 use very small samples, for tests that are slow, expensive or destroy the product.
Our guide to pre-shipment inspection and AQL explains defect classes and what to do when goods fail, and our quality inspection service carries out AQL inspections at factories across China.
Common questions
What sample size do I need for 3,000 units?
At General Inspection Level II, a lot of 3,000 units uses code letter K, a sample of 125 units. At AQL 2.5 the lot passes with up to 7 major defects and fails at 8.
What does AQL 2.5 mean?
It's the acceptance quality limit used to choose the sampling plan. In practice it sets how many major defects the sample can contain before the order fails.
Is this calculator based on ISO 2859-1?
Yes. It uses the ISO 2859-1 (equivalent to ANSI/ASQ Z1.4) tables for single sampling and normal inspection, at all general and special inspection levels.