Acceptable Quality Limit (AQL) is a sampling method used to determine how many defects are permitted within an inspected portion of a production lot. It provides a consistent way to evaluate product quality without checking every unit.

ECQA AQL Sampling Calculator

The AQL Sampling Calculator helps determine the required sample size and the allowable defect counts using ISO-based sampling rules. It supports General Inspection Levels I, II, and III and provides quick guidance for common AQL values used in product inspections.

How to Use the AQL Sampling Calculator

The calculator requires three inputs. After entering the values, it will display the corresponding sampling plan.

1. Lot Size

Enter the total production quantity. This value determines the sample size code letter defined by ISO 2859.

2. Inspection Level

Select the inspection level.

• General Level II is commonly used and provides balanced sampling for most products.
• General Levels I and III provide reduced or tightened sampling.
• Special Levels are used for limited or specific tests.

3. AQL Values

Choose the AQL levels for the defect categories: critical, major, and minor.
Examples of common values:

• Critical: Use the lowest available level in the calculator (for example, 0.65%) to represent a very strict standard.
• Major: 1.0 to 2.5
• Minor: 4.0 to 6.5

After the inputs are selected, the calculator displays the sample size and the maximum number of allowable defects for each category.

Example: 

A shipment of 2,000 T-shirts is ready for inspection.
Enter 2,000 as the lot size and select General Level II.
Set AQL 0.6 for critical defects, 2.5 for major defects, and 4.0 for minor defects.
The calculator displays the required sample size and the allowed defect limits for this inspection.

AQL Sampling Chart

The sampling chart provides a reference for identifying code letters, sample sizes, and acceptance limits. It reflects the structure of ISO 2859. Learn How to Read an AQL Sampling Table

Download Free AQL sampling chart

How AQL Works

AQL uses statistical sampling to evaluate whether a batch meets preset quality limits. Inspectors select a sample of units from the production lot and classify defects into specific categories. The number of defects found is then compared with the limits defined by the selected AQL level.

If the defect count is within limits, the batch passes. If it exceeds the limit, the batch fails.

AQL does not estimate total defects in the entire lot. It provides a standardized decision method for inspection.

How to Choose the Right AQL Level

Selecting the correct AQL level depends on the product type, supplier capability, and the level of risk you can accept. The following factors help determine the most appropriate AQL for your inspection.

Product criticality

Safety-related products such as medical devices or automotive parts require stricter AQL levels to minimize the possibility of defects.

Product complexity

Products with multiple components or complex functions benefit from lower AQL thresholds to ensure all elements meet the required standards.

Supplier history

Reliable suppliers with stable quality performance may allow the use of a more flexible AQL. New or inconsistent suppliers usually require stricter limits.

Risk tolerance

If your tolerance for defects is low, especially for premium products or strict markets, a lower AQL is recommended.

Inspection costs

Higher AQL values generally require smaller sample sizes and reduce inspection time. Businesses balance quality needs with available budget when selecting AQL levels.

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ECQA provides technical guidance on selecting sampling plans, defining defect classifications, and applying AQL consistently across inspections. Contact ECQA for more information.