How AQL sampling works, which defect limits to choose, what a pre-shipment inspection checks and how to act on the report before you release payment.
Checking every unit of a large order is rarely practical. AQL (Acceptance Quality Limit) sampling lets an inspector check a statistically defined sample and decide whether the whole lot is acceptable. It is the most common method for inspections in China, and understanding it helps you read reports and set the right limits.
What AQL means
AQL sampling comes from the ISO 2859-1 standard (equivalent to ANSI/ASQ Z1.4). Based on the lot size and the inspection level, the tables give:
- The sample size: how many units the inspector picks at random.
- The acceptance number: the maximum number of defective units allowed for the lot to pass.
- The rejection number: the number of defective units at which the lot fails.
Most consumer product inspections use General Inspection Level II.
Classifying defects
Defects are usually split into three classes, each with its own limit:
| Class | Example | Common limit |
|---|---|---|
| Critical | Sharp edges, electrical safety risk, mold | 0 (not accepted) |
| Major | Product does not work, wrong color, broken part | AQL 2.5 |
| Minor | Small cosmetic marks, loose thread | AQL 4.0 |
These limits are common, not mandatory. Premium products often use tighter limits, for example 1.5 for major defects.
An example
For a lot of 1,201 to 3,200 units at General Level II, the sample size is 125 units. With AQL 2.5 for major defects, the lot passes with up to 7 major defects and fails with 8 or more. With AQL 4.0 for minor defects, it passes with up to 10 and fails with 11 or more.
What a pre-shipment inspection checks
A pre-shipment inspection takes place when at least 80% of the goods are finished and packed. A typical checklist includes:
- Quantity: finished and packed units against the order.
- Workmanship: visual check of the sample for defects.
- Specifications: dimensions, weight, color and materials against the approved sample.
- Function tests: product-specific tests, for example assembly, operation or drop tests.
- Packaging and labeling: carton markings, barcodes, warning labels and the instructions your market requires.
Before the inspection
- Share an approved golden sample or detailed photos with the inspector.
- Write a checklist with your specific tests and tolerances.
- Agree with the supplier, in the contract, that the shipment depends on passing the inspection.
Reading the report and acting on it
The report should include the result, the defects found by class, photos and measurements. If the lot fails, the usual options are:
- Rework and re-inspection at the supplier’s cost.
- Sorting of the whole lot to remove defective units.
- Negotiating a discount if the defects are acceptable for your market.
The key is to inspect before paying the balance. After payment, your leverage is much lower.
Beyond the final inspection
For new suppliers or complex products, add checks earlier in the process: a pre-production check of materials and an inspection during production can catch problems while they are still cheap to fix.
Zyntral includes AQL quality control in its End to End import service, with photos and a detailed report before goods leave the factory. If you want to understand where inspection fits in the full process, read 10 ways to import from China.
