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Conducting a Quality Inspection with AQL

By June 7, 2024June 14th, 2024Quality Control9 min read

A Guide To Conducting A Quality Inspection

Using The Acceptable Quality Limit (AQL) Process

What is an AQL inspection, and why is it used?

‘AQL’ stands for ‘Acceptance Quality Limit‘, and is defined as the “quality level that is the worst tolerable” in ISO 2859-1. The AQL inspection represents identifying the maximum number of defective units, beyond which a batch is rejected.

By following this inspection standard you can quickly determine the overall quality of the batch and help decide whether it meets the acceptable standards or not.

The difference between Special and General AQL Inspections.

In AQL inspections, special and general inspections serve different purposes and are used under varying circumstances to ensure the quality of a batch.

General Inspections

When Used:
  • General inspections are the default and most commonly used for standard quality checks.
  • They are typically applied to routine inspections where there are no specific concerns or heightened requirements.
Why Used:
  • General inspections provide a broad overview of the batch’s quality.
  • They strike a balance between thoroughness and efficiency, ensuring that the sample size is statistically significant without being overly large or small.
  • This level of inspection is sufficient for most products under normal conditions.

Special Inspections

When Used:
  • Special inspections are used when there are specific quality concerns or higher risk factors.
  • They are often employed for critical components, high-value items, or when stricter quality control is required.
  • Special inspections might be used if previous inspections have revealed issues, prompting more detailed scrutiny.
Why Used:
  • Special inspections allow for a more detailed and focused examination of specific aspects of the batch.
  • They can involve different levels (S-1 to S-4), each representing a varying degree of scrutiny, from lighter to more intensive inspection.
  • These inspections are useful for detecting defects that might not be apparent during general inspections, thereby ensuring higher quality and reducing risk.


  • General Inspections: Used for routine checks, balancing thoroughness and efficiency, providing a broad quality assessment.
  • Special Inspections: Used for higher-risk or critical items, offering detailed scrutiny to ensure stringent quality standards are met.

By choosing the appropriate type of inspection based on the situation, you can effectively manage and maintain product quality, minimizing risks and ensuring customer satisfaction.

AQL Chart

Step 1

Setting Up A Sampling Plan

First, you need to determine the type of inspection you wish to perform for your batch. This will dictate how many samples to inspect and what percentage of defects will be considered acceptable.

For this guide, we use AQL General Inspection Level II, the standard level used by Colourstone.
This includes a maximum acceptance of:

  • 4% Inspection Level on Minor defects,
  • 2.5% Inspection Level on Major defects,
  • 0.065% Inspection Level on Critical defects.

Using our AQL chart, we can calculate the number of units to inspect (Units in Sample) based on the total number of units in the batch and determine the maximum acceptable number of defects.
Refer to the following table for guidance:

Total Units in
Sample Level
Units in
Minor Defects (Max) Major  Defects (Max) Critical  Defects (Max)
501-1,200 J 80 7 5 0
1,201-3200 K 125 10 7 0
3,201-10,000 L 200 14 10 0
10,001-35,000 M 315 21 14 0
35,001-150,000 N 500 21 21 1
150,001-500,000 P 800 21 21 1
500,001+ Q 1250 21 21 2

Step 2

Randomly Selecting the Sample Units

Now that we know how many samples from the batch need to be inspected, we need to gather the sample units.

To get a true representation of the batch, ensure that your random selection covers different sections. For example, obtain samples from the top, middle, and bottom of the pile (carton or pallet). This prevents selection bias and provides a good indication of the overall batch quality.

Step 3

Inspecting the Sample Units

Once you have gathered your sample units, it is time to evaluate them for quality. Specific quality requirements should be clearly stated between the buying and selling parties before starting a production order. These requirements can include branding and color matching, print registration, packaging, etc.

Use the following steps to assist your inspection:

  1. Reference Quality Policies: If applicable, refer to your product’s quality policy or prerequisites for specific inspection criteria.
  2. Examine Each Sample: Inspect each sample and note any defects, classifying them as:
    • Minor Defects: These are slight deviations from the specifications that most users are unlikely to notice or mind.
    • Major Defects: These are significant issues that make the product unacceptable to the end user.
    • Critical Defects: These are severe problems that are completely unacceptable; they could harm the user or violate regulations.
  3. Document Defects: Take photos of defective units for review.

Step 4

Calculate Defective Sample Units

Add up the total number of defects found to the maximum allowed in your AQL chart for Minor, Major and Critical:

  • If defects are below the maximum: ✅ The batch passes the AQL inspection.
  • If defects exceed the maximum: ❌ The batch fails the AQL inspection. Report the issues immediately.

Step 5

Reporting a Failed Inspection

In the case the defects exceed the maximum, you must act quickly and present your claim.
Leaving it too late to report quality issues may void your claim, as some suppliers require claims to be made within a certain time frame of goods handed over.

Ensure you:

  1. Document all defects, including defect type, severity, total affected units, and photos in your report
  2. Understand that manufacturers often produce extra units to account for defects. You should account for this in your assessment.

💡Important To Note

Machines operate at very high speeds, and the ‘make-ready’ or ‘start-stop’ machine process can deliver a small quantity of defects that cannot be removed.
Therefore, it is common for most manufacturers to produce extras in their batch to cover these potential defects, which can range from 2% t0 10% on average.
It is important that the over supplied quantity is considered in your assessment of the batch quality before making your claim.

Step 6

Next Steps for Issue Resolution

In the print and packaging industry, if the defect samples inspected exceed the maximum accepted amount for minor, major, or critical defects in an AQL test, the next course of action typically involves several steps. Here’s a general outline of what usually happens:

  1. Notification and Documentation:
    • The buyer immediately informs the supplier about the inspection results.
    • Detailed documentation of the defects is provided, including photos and descriptions.
  2. Root Cause Analysis:
    • The supplier conducts a root cause analysis to determine why the defects occurred.
    • This may involve reviewing production processes, materials used, and quality control procedures.
  3. Corrective Actions:
    • The supplier implements corrective actions to address the root cause of the defects.
    • This may include adjustments to the production process, retraining staff, or improving quality control measures.
  4. Re-inspection:
    • Depending on the severity and type of defects, a re-inspection of the batch might be required.
    • The re-inspection can be a full inspection of the entire batch or a more extensive sampling to ensure the issues have been resolved.
  5. Decision on the Batch:
    • If the defects are severe (especially critical defects), the entire batch may be rejected.
    • For minor defects, the batch might be accepted with the agreement that the supplier will provide compensation or correct the issues in future orders.
    • In some cases, the supplier might be required to rework the batch to meet the quality standards.
  6. Remake or Refund:
    • If the batch is rejected, the supplier may need to remake the products according to the agreed quality standards.
    • Alternatively, a refund or credit might be issued to the buyer.
  7. Quality Assurance Review:
    • Both the buyer and the supplier review and revise the quality assurance processes to prevent similar issues in the future.
    • This could include updating the quality standards, inspection criteria, and communication protocols.
  8. Alternative Actions

    • Conduct A Full Inspection: In cases where major or critical defects are found, a full inspection of the batch might be necessary to identify all defective units.
    • Increased Sampling: For minor defects, increasing the sample size in subsequent inspections can help ensure that the batch quality improves.
    • Third-Party Inspection: Sometimes, an independent third-party inspection service may be employed to provide an unbiased assessment of the batch quality.


By following these steps, you can effectively perform AQL inspections and ensure high product quality from your suppliers. This guide provides a comprehensive overview of running a quality inspection using the AQL procedure, helping you maintain high standards and avoid potential issues with your suppliers. If such issues are recurring, it may be worth considering switching suppliers.

If you need help implementing AQL procedures in your workplace or would like to download any of this information into a report manual, please contact us for support.

Reach Out Today
John Kokkinos

Born and raised in Melbourne, John's roots in the packaging and printing industry run deep, shaped by a family legacy of craftsmanship and innovation. With over three decades of dedicated experience, he has honed his expertise in print packaging, demonstrating exceptional skill in managing production lines with finesse. John's professional journey has led him to China, where he spent more than 20 years spearheading the establishment and optimisation of packaging facilities. Renowned for his leadership and industry acumen, he has earned a reputation as a trusted leader and innovator in the field.