Acceptable Quality Level (AQL)

The acceptable quality limit (AQL) is defined in ISO 2859-1 as the “quality level that is the worst tolerable.” Basically, the AQL tells you how many defective components are considered acceptable during random sampling quality inspections. It is usually expressed as a percentage or ratio of the number of defects compared to the total quantity.

Goods in a sample are tested at random, and if the number of defective items is below the predetermined amount, that product is said to meet the acceptable quality level (AQL). If the acceptable quality level (AQL) is not reached for a particular sampling of goods, manufacturers will review the various parameters in the production process to determine the areas causing the defects.

As an example, consider an AQL of 1% on a production run. This means that no more than 1% of the batch can be defective. If a production run consists of 1000 products, only 10 products can be defective. If 11 products are defective, the entire batch is scrapped. This figure of 11 or more defective products is known as the rejectable quality limit (RQL).

The acceptable quality level (AQL)is an important statistic to companies seeking a Six Sigma level of quality control. Acceptable quality level is also known as the acceptable quality limit.

The acceptable quality level (AQL) of a product can vary from industry to industry. For example, medical products are more likely to have more stringent AQL because defective products can result in health risks. In contrast, a product with benign side-effects of a possible defect may have a less strict AQL, such as the remote control for your TV. Companies have to weigh the added cost associated with the stringent testing and potentially higher spoilage due to a lower defect acceptance with the potential cost of a product recall.

In 2008 the usage of the abbreviation AQL for the term "acceptable quality limit" was changed in the standards issued by at least one national standards organization(ANSI/ASQ) to relate to the term "acceptance quality level." It is unclear whether this interpretation will gain general usage, but the underlying meaning remains the same.

Customers would, of course, prefer zero defect products or services—the ideal acceptable quality level. However, sellers and customers usually try to arrive and set acceptable quality limits, based on factors typically related to business, financial, and safety concerns.

AQL varies from industry to industry and product to product. Companies dealing with medical tools, for example, would have more stringent AQL. AQL is an important statistic for companies seeking Six Sigma level of quality control.

Instances of failure to meet customer quality requirements is termed as defects. In practice, there are three categories of defects:

Critical Defects: Defects, when accepted could lead to harm the users. Such defects are totally unacceptable. It is defined by 0% AQL.

Major Defects: Defects usually not acceptable by the end users, as it is likely to result in failure. The AQL for major defect is 2.5%.

Minor Defects: Defects, which are not likely to reduce materially the usability of the product for its intended purpose but slightly differs from specified standards. Some end users still go ahead and buy such products. The AQL for minor defects is 4%.

Acceptable Quality Level (AQL): AQL is typically considered to be the worst quality level that is still considered satisfactory. It is the maximum percent defective that can be considered satisfactory. The probability of accepting an AQL lot should be high. A probability of 0.95 translates to a a risk of 0.05.

Rejectable Quality Level (RQL): This is considered unsatisfactory quality level and is sometimes known as lot tolerance percent defective (LTPD). This consumer’s risk has been standardized in some tables as 0.1. The probability of accepting an RQL lot should be low.

Indifference Quality Level (IQL): This quality level is somewhere between AQL and RQL.

Different companies maintain different interpretations of each defect type. In order to avoid argument, buyers and sellers agree on an AQL standard that is appropriate to the level of risk each party assumes, which they use as a reference during pre-shipment inspection.