AQL – ACCEPTABLE QUALITY LIMIT | COMPLETE GUIDE 2021
If you are planning to conduct a product inspection, you may have come across the term AQL. If you haven't, then this is a term you have to familiarise yourself with if you plan to have a product inspection.
In this article we will attempt to explain what AQL is and how it works. We will use simple examples and and go through a case study in which we compare an inspection using an AQL sampling methodology, with a full inspection.
By the end of this article, you will know everything there is to know about AQL sampling and how to use the 2 famous AQL tables.
We know that our readers are busy and have therefore split the article into different sections. Feel free to read the full content, or just the sections that is of interest to you.
Estimated reading time: 3-5 mins
The article is divided into the following 7 sections:
- What is Acceptable Quality Limit (AQL)
- AQL Tables - How to Read Them and How They Work?
- What about defects that can harm customers?
- Why is AQL Preferred Over Conducting a 100% Inspection?
- Case Study - AQL vs Full Inspection
- Can AQL Guarantee That A Shipment Has Zero Defects?
- Summary
- Bonus: How do I determine the right AQL level and acceptance number for my specific shipment?
What is Acceptable Quality Limit (AQL)
AQL stands for Acceptable Quality Limit and is a sampling methodology used to determine three things during an inspection.
- The number of units to inspect, also called the AQL sample size
- The number of units with minor defects that will deem a “FAIL” result
- The number of units with major defects that will deem a “FAIL” result
This is a more structured way to organise inspections as you will know what to look for.
The results from an inspection will be aggregated into a report after an inspection. This allows the importer to make an informed decision on whether to accept or reject the entire product batch.
An inspection report lists all results with pictures and data points. It also clearly states whether a shipment has passed or failed the chosen Acceptable Quality Limit.
The report was created for one of our customers who ordered a pre-shipment inspection.
AQL Tables - How to Read Them and How They Work
The following two tables are used to determine the AQL sample size to be inspected and the maximum allowed number of defects.
The AQL tables can look a bit confusing at first glance, but are very intuitive once you understand how they work. We have provided an explanation below each AQL table.
Let’s assume that you have ordered a quantity of 20.000 units and chosen AQL level II(See table above). This means that your batch size falls between 10,0001-35.000 units on the left side column(Underlined in red).
If we follow along the line horizontally to the column General Inspection Level II, we end up on the letter code M. We will use this letter when looking into table 2 below
We will now continue by searching for the letter code “M” in the first column on the left side(underlined in red) in table 2. We then move along the same row to the second column to find the AQL sample size(circled in red). Wee see that the sample size for this inspection is 315 units.
Important:The inspector should pick the samples from different cartons, preferably all of the cartons to avoid inspection results that are biased towards the products in only one carton. This is because the products in one carton may not be representative for the entire product order.
We see the different AQL levels on the right hand-side of the two columns in table 2. The vast majority of inspections conducted on consumer products use level 2.5 for major defects and 4.0 for minor defects. This part of the table is used to determine the maximum allowed number of defects.
The inspection will deem the result as failed if the sample size has 15 major defects or more. If the sample has 14 major defects or less, the inspection will pass, according to the column with AQL level 2.5.
The inspection will deem the result as failed if the sample size has 22 minor defects or more. If the sample has 21 minor defects or less, the inspection will pass, according to the column with AQL level 4.0.
In summary, the inspection will fail if either of the following number of defects are found:
- 15 major defects or more
- 22 minor defects or more
The AQL methodology provides clear guideline on when your inspection company should fail or pass an inspection.
What about defects that can harm customers?
The AQL tables do not mention critical defects in their tables. A critical defect is one that could cause injury to a customer or even death.
There is zero tolerance for critical defects under AQL. A shipment with only one critical defect unit will therefore fail an inspection.
Why is AQL Sampling Preferred Over Conducting a 100% Inspection?
A common question we receive from our clients is “Why do you recommend inspecting only a sample instead of 100% of our products?”.
The answer is simple, inspecting an entire batch is expensive. An inspector is paid based on the time required to conduct an inspection.
An inspection conducted by professional inspectors takes time. The inspectors follow international guidelines and look over several details such as damages, defects, colour fading, odour, functionality, aesthetics, label readability and more. This is looked for on each unit that is inspected. You can read more about our pre-shipment inspection process.
Case Study - AQL vs Full Inspection
Let’s assume that you have just manufactured 20.000 units of a wallet and that an inspector is able to inspect about 500 units per day.
Now, let’s compare an inspection following AQL with a 100% inspection:
Case 1: AQL Inspection
In this case we will decide on AQL level II and 2.5 as the acceptable quality level. This is the standard choice for the majority of inspections.
If we take a look at the AQL tables we see that we need to look for the letter code “M” in the second table. If we take a look at the second table, we see that we need to pick an AQL sample size of 315 units. This will take 1 day.
The Total Price = Price per Day x Number of days = 299 USD/day * 1 day = 299 USD
This is equivalent to 0.015 USD per unit. (299 USD / 20.000 units = 0.015 USD). This will not have any large impact on your product cost
Case 2: 100% Inspection
In this case we will first need to estimate the number of days needed to inspect all the products. We then calculate the total price for inspecting all the products.
Number of days needed = Number of units / number of units an inspector can inspect in one day =
20.000 units / 500 units per day = 40 days
The Total Price = Price per Day x Number of days = 299 USD/day * 40 days = 11.960 USD
This is equivalent to 0.6 USD per unit. This will have a significant impact on your margins.
Comparison:
The total price is 40 times higher for a full inspection than for an AQL inspection.
Can AQL Guarantee That A Shipment Has Zero Defects?
As you might have guessed by now, the simple answer is “no, you cannot ensure zero defects with an AQL sample inspection”. AQL stands for Acceptable quality limits and is by definition not designed to ensure zero defects.
It would be unreasonable to expect zero defects from a manufacturer for the majority of manufactured products. The aim of the AQL sampling methodology is to design an inspection plan that will detect if the manufacturer has a higher defect percentage than what acceptable.
Remember that AQL has been an industry standard for several decades for a reason. The vast majority of large retailers worldwide strictly follows this standard.
The standard AQL levels used to determine the sample size and the maximum allowed number of defects are:
- AQL level II from table 1
- Acceptable Quality Level 2.5 for major defects from table 2
- Acceptable Quality Level 4.0 for minor defects from table 2
Before production, we recommend that you make an agreement with your factory to come to a mutual understanding of what results you consider an acceptable results.
We also recommend agreeing on how to deal with a scenario in which a shipment fails an inspection. For example: If the shipment fails the inspection, the factory has to fix the defects and to cover the cost for a new pre-shipment inspection.
Summary
AQL is a widely used standard for choosing a sample size to be inspected, and the number of defects that has to be found in order to deem the results of the inspection as “FAIL”.
AQL sampling is preferred over a 100% inspection of all of the units. This is because a random sample inspection will give a good indicator on whether the entire batch has an excessive amount of defects.
A full inspection can be very expensive. In our case study we saw that a full inspection would cost 40 times more than a standard AQL inspection for an order size of 20.000 units.
To determine the sample size to be inspected and the maximum allowed number of defect units, we use the two AQL tables.
The first AQL table is used to find a letter code based on the quantity of your order. The letter code found in the first AQL table is used to find the right letter code, and hence the sample size in the second table.
The acceptable quality levels in the second table determines the maximum allowed number of defect units.
The Standard AQL level used is level II in table 1, and level 2.5 and level 4.0 in table 2 for major defects and minor defects respectively.
If the shipment has either an excessive amount of Major defects or an excessive amount of Minor defects the inspection will deem a FAIL result.
How do I determine the right AQL and Acceptance number for my specific shipment?
Our trained account managers will be available to ensure you choose the inspection level and AQL values that best suit your needs. Inspection Bird’s inspectors comply with the internationally recognized ISO 2859-1 standard when conducting product inspection, .
This international standard is widely used in the quality assessment industry and with equivalents in all countries’ worldwide. The standard is published by the International Organization for Standardisation (ISO).
If you have any questions about our inspection services, or if you need help with setting up an inspection at your factory, please do not hesitate to contact us on [email protected].
