Understanding Sampling Method and AQL in Random Product Inspection

By Veriquality Source:

Understanding Sampling Method and AQL in Random Product Inspection

Some importers, who are new to quality control, may misunderstand that every piece of production should be inspected before shipment. It may be a wise choice for high value products or for shipments that tend to have very high quality risks or for really picky customers. For example, it is very common for Japanese customers to choose 100% full piece by piece inspection.


However, sometimes 100% full inspection is just not workable because it is too costly and time-consuming, which may impair your margin and affect the shipping schedule. Moreover, without prior agreement most factories would be reluctant to receive 100% full inspection.


In fact, for most shipments, a random inspection with statistically reasonable sample would be sufficient to meet your expectations. So how to determine a fair and rational sample size and also an acceptance level for such random inspection? There is where AQL standard should be introduced, which helps you determine whether to accept or reject a shipment based on the number and type of defects found in the pre-determined sample size.

Here are some definitions before you study the AQL tables

Acceptable Quality Level (AQL): also called Acceptable Quality Limits, is defined as the maximum percent defective that, for purpose of random sampling inspection, can be considered satisfactory as a process average.

Inspection Levels: The AQL tables provide for three general inspection levels and four special inspection levels. These seven levels permit the user to balance the cost of inspection against the amount of protection required.

Sampling Plans: A lot sampling plan is a statement of the sample size or sizes to be used and the associated acceptance and rejection numbers.

Critical Defects: likely to result in unsafe condition or contravene mandatory regulation or reject by import customs.

Major Defects: reduces the usability/function and/or sale of the product or is an obvious appearance defect.

Minor Defects: doesn't reduce the usability/function of the product, but is a defect beyond the defined quality standard more or less reduces the sale of the products.

Generally, the Critical/Major/Minor defects are defined as above and in practice specific circumstances and client requirements may also be taken into consideration.

There are two AQL tables. The first one tells you which ‘code letter’ to use based on the lot size and selected sampling plan, such as S-4, G-I, G-II, etc. (the most commonly used inspection level for consumer goods is General Inspection Level II).

For example, I assume your ‘lot size’ (which means quantity) is between 3201pcs and 10,000pcs, and that your inspection level is ‘II’. Consequently, the code letter is “L”.

Then, the second table will give you the sample size and the maximum numbers of defects that can be accepted based on the selected code letter. Ac means accepted; Re means rejected

But, What Sampling Plan and AQL Suits You and Your Products?

Sampling plan: you will find 7 levels from G-III (highest) to S1(lowest). A higher inspection level corresponds to a larger sample size, with GIII being the highest.

Although you can choose either level based on the following factors:

-       Your budget for a specific shipment

-       Value or price of the products to be inspected

-       Expected quality risk, including previous performance of the factory, is it a repeat order or a new design

-       Some other factors like time window between inspection to shipment, factory’s agreement with a larger sample size (considering they need to unpack and repack the products)

In practice, for most consumer products including garments, textiles, gifts, toys, furniture, houseware, etc., G-II are mostly commonly used and widely accepted by factories for a random inspection.

There are also cases that customers may want to determine based on the percentage % of shipment quantity rather than defined sampling levels, e.g. 10% of total quantity, that would be fine. But in that case, there would be no corresponding defined acceptance criteria and customers have to make its own judgement on how many defects are acceptable or not.

Acceptance Criteria (AQL): the lower value is chosen, the stricter the acceptance criteria is, with 0.065 as the strictest. As a common sense, you cannot expect a mass stock of 2000pcs is defect free (even for iPhone or other luxury clothes or bags), therefore it is reasonable that you should have an acceptable defect rate in mind.

For customers with little knowledge, here are mostly commonly used AQLs for reference:

-       Critical: 0, Major: 2.5, Minor: 4.0 for inspection of garments, textiles, furniture, houseware, sporting goods, gifts, toys, etc.

-       Critical: 0, Major 1.5, Minor 4.0 for inspection of consumer electronics and household appliance, etc.

It should be noted that for some products a different sampling method or acceptance limit may be more appropriate. For example, 4-point system or 10-point system other than AQL tables included here is usually adopted for fabric inspection.


While 100% inspection (defect sorting and removal) provides largest assurance to buyers as regards to quality, it is not always recommended due to the budget, time and future cooperation with factories. In most cases, you can always gather enough information from a random inspection with a reasonable sample size, so as to make a well-informed decision on the whole order.

Each customer may choose its own sampling plan and AQL based on its unique circumstances. It is advisable to share your requirements to the third-party inspection agent you use in the early stage. If you don’t know, the third-party inspection agent  like Veriquality may propose the sampling plan and AQL based on their experience and what they know of you. In that case, after some inspections have been done, you may further determine whether it is necessary to make adjustments when you are getting more familiar with these methods and concepts.