What is AQL?
AQL (Acceptable Quality Level) is a statistical sampling method used worldwide for quality inspections. Rather than checking every single product (which is impractical for large orders), AQL uses random sampling to determine if a batch meets quality standards.
AQL is defined in ISO 2859-1 (also ANSI/ASQ Z1.4) and is the industry standard for quality control inspections.
The AQL number represents the maximum acceptable defect rate. For example, AQL 2.5 means you'll accept batches where defects don't exceed approximately 2.5% of the lot.
Inspection Levels
There are three general inspection levels:
Level I (Reduced)
- Smallest sample size
- Use when: Established suppliers with good track record, low-risk products
- Provides less protection but saves time
Level II (Normal)
- Standard sample size
- Use when: Most inspections, new suppliers, normal risk
- Recommended default for most situations
Level III (Tightened)
- Largest sample size
- Use when: Quality problems expected, critical products, new product launches
- Provides maximum protection
Most QC inspections use Level II.
AQL Values
Common AQL values and typical uses:
AQL 0.65 (Very Strict)
- Critical defects (safety issues)
- Medical devices, safety equipment
- Defects that could cause harm
AQL 1.0 (Strict)
- Major defects
- High-value products
- Defects affecting function or usability
AQL 2.5 (Standard)
- Minor defects
- Most consumer goods
- Cosmetic issues that don't affect function
AQL 4.0 (Lenient)
- Minor cosmetic defects
- Low-cost items
- Defects barely noticeable
Many inspections use multiple AQL levels:
- Critical defects: AQL 0.65
- Major defects: AQL 2.5
- Minor defects: AQL 4.0
Sample Sizes
Sample size depends on batch size and inspection level. Examples using Level II:
| Batch Size | Sample Size |
|---|---|
| 2-8 | 2 |
| 9-15 | 3 |
| 51-90 | 13 |
| 281-500 | 50 |
| 1201-3200 | 125 |
| 10001-35000 | 315 |
For a batch of 5,000 units at Level II, you would inspect 200 random samples.
Use our AQL Calculator to determine exact sample sizes for your batch.
Accept/Reject Criteria
For each sample size and AQL level, there are accept and reject numbers:
- Accept (Ac) - If defects found ≤ this number, batch passes
- Reject (Re) - If defects found ≥ this number, batch fails
Example: For 200 samples at AQL 2.5:
- Accept: 10 defects
- Reject: 11 defects
If you find exactly 10 or fewer defects, the batch passes. If you find 11 or more, it fails.
What Happens When a Batch Fails?
Options include:
- Reject the entire batch - Don't ship, request rework
- 100% inspection - Check every unit, remove defectives
- Rework - Factory fixes defects, re-inspection follows
- Negotiate - Accept with price reduction for minor issues
Ready to implement proper QC? Learn about our inspection services.