An AQL table (Acceptable Quality Level table) is the reference chart used in quality control to select sample sizes and acceptance/rejection numbers for lot inspections. Grounded in ISO 2859-1 (international) and ANSI/ASQ Z1.4 (U.S.), it lets you evaluate a large production lot by testing only a small, statistically valid sample—keeping risk under control while avoiding 100% inspection.
What an AQL Table Does (and Why It Matters)
An AQL table translates three inputs into a concrete sampling plan:
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Lot (batch) size – total units produced in the run.
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Inspection level – how intensively you want to check (e.g., General I/II/III or Special S-1 to S-4).
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AQL values – the maximum defect rates you’ll tolerate for each class of defect (typically 0.0% critical, 2.5% major, 4.0% minor for consumer goods).
From those inputs, the table gives you:
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A sample size code letter (e.g., “K”).
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The sample size to inspect (e.g., 125 units).
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The accept (Ac) and reject (Re) numbers for each defect class (e.g., at AQL 2.5% major: Ac = 7, Re = 8).
Why it matters: AQL tables balance cost and risk. They prevent under-inspecting (letting bad lots through) and over-inspecting (wasting time/money), and they create a shared, objective standard between buyer and supplier.
Key Concepts You Need to Know
Defect Categories
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Critical: Safety/legal hazards; AQL is typically 0.0 (zero tolerance).
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Major: Likely to make the product unsellable or fail in use (e.g., functional issues, obvious cosmetic flaws).
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Minor: Slight imperfections that don’t affect form/fit/function.
Inspection Levels
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General I / II / III: Default intensity for most inspections. General II is the standard starting point.
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Special S-1 to S-4: Used for small, targeted checks (e.g., labeling, color, special attributes) when a full sample isn’t needed.
AQL Values (Typical Starting Points)
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Critical: 0.0
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Major: 2.5
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Minor: 4.0
Adjust up/down based on product risk, brand positioning, and regulatory context.
How to Use an AQL Table (Step-by-Step)
1) Define the Inputs
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Lot size: Example, 8,000 units.
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Inspection level: Start with General II.
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AQLs: Critical 0.0 / Major 2.5 / Minor 4.0.
2) Find the Code Letter
Open the AQL table (ISO 2859-1 / ANSI Z1.4). In the General II row and your lot size column, find the code letter (e.g., “L”).
3) Read the Sample Size
In the second part of the table, locate code letter L to get the sample size (for example, 200).
4) Apply AQLs to Get Ac/Re
For each defect class and its AQL, read the Accept (Ac) and Reject (Re) numbers:
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Critical (0.0 AQL): Ac = 0, Re = 1 (any critical defect fails).
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Major (2.5 AQL): e.g., Ac = 10, Re = 11.
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Minor (4.0 AQL): e.g., Ac = 14, Re = 15.
(Exact Ac/Re depends on the standard table; the values above illustrate the logic.)
5) Inspect and Decide
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Inspect 200 randomly selected units.
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Count critical/major/minor defects separately.
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If any defect class exceeds Re, the lot fails.
Practical Tips for Importers and QA Teams
Choosing the Right AQLs
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High risk / regulated goods (toys, medical): Tight AQLs (e.g., Major 1.0–1.5; Minor 2.5–4.0).
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Premium brands: Lower AQLs to protect perception.
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Commodity goods: Standard (Major 2.5, Minor 4.0) is common.
When to Use Special Levels (S-1 to S-4)
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Labeling, barcodes, inserts, quick checks where a smaller sample is sufficient.
Integrate AQL with QA (Prevention)
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AQL is detection; combine it with QA prevention tools:
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Clear specs (dimensions, tolerances, Pantone, BOM).
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Golden sample approved by both parties.
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PFMEA & Control Plan for process control.
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DUPRO (During-Production) to catch drift early.
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CAPA/8D after failures.
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Worked Examples
Example A — Medium Lot, Standard Settings
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Lot size: 3,200 units
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Level: General II → Code letter K (example)
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Sample size: 125
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AQLs: Critical 0.0 / Major 2.5 / Minor 4.0
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Ac/Re (illustrative):
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Critical: 0/1
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Major: 7/8
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Minor: 10/11
Decision: If you find 8 major defects → Fail (Re reached).
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Example B — Small Lot, Special Check
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Lot size: 420 units
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Level (labels only): S-3 → smaller sample (e.g., 20)
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AQL (labels as minor): 4.0
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Ac/Re (illustrative): 1/2
Decision: 2 labeling errors → Fail.
Note: Always consult the official ISO 2859-1 / ANSI Z1.4 tables your team or provider uses; Ac/Re values vary by sample size and AQL.
Common Mistakes to Avoid
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No alignment on definitions: If “major vs minor” isn’t defined in writing, disputes are inevitable.
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Mixing defects: Track counts by class; do not lump all defects together.
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Skipping DUPRO: Waiting for final inspection lets problems multiply.
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Changing AQL mid-order: AQLs must be fixed before production.
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Non-random sampling: Convenience sampling invalidates results.
Advanced Notes
Tightened / Reduced Inspection
Standards include switching rules: if recent lots fail, move to tightened inspection; if they pass consistently, move to reduced. This keeps effort proportional to risk.
Zero Acceptance Plans (C=0)
For critical safety items, some buyers use C=0 (no critical defects accepted and very small acceptance for majors/minors). This is stricter than typical AQL.
Integration with Capability (Cp/Cpk)
Mature suppliers pair AQL with SPC and capability goals (e.g., Cpk ≥ 1.33 pre-launch), reducing defect creation rather than merely detecting it.
Quick Checklist for Implementation
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Agree AQLs by defect class (Critical/Major/Minor).
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Fix inspection level (start with General II).
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Embed Ac/Re numbers in the PO/Quality Agreement.
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Ensure random sampling and separate counts by defect class.
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Pair AQL detection with QA prevention (PFMEA, Control Plan, DUPRO, CAPA).
With the AQL table used correctly—and supported by strong preventive QA—your inspections become faster, fairer, and far more effective at protecting your brand.
FAQ — AQL Table
What does “AQL” actually mean?
It’s the maximum defect level you’re willing to accept in a lot, expressed per defect class, used to set accept/reject criteria on a statistically valid sample.
Which inspection level should I pick?
Start with General II. Use General III for higher risk or more scrutiny, and General I if you need a lighter check. Use Special levels (S-1 to S-4) for targeted attributes.
Can I have different AQLs for different defects?
Yes. Most buyers set Critical 0.0, Major 2.5, Minor 4.0 as a baseline, then adjust by risk.
Does passing AQL guarantee zero defects in the shipment?
No. AQL gives statistical confidence, not certainty. It’s risk-based control, not perfection.
How big is the sample?
Depends on lot size and inspection level. The table converts these into a code letter and sample size.
Is AQL the same as acceptance sampling?
AQL is part of acceptance sampling plans defined in ISO 2859-1 / ANSI Z1.4.
How do I reduce failure rates?
Pair AQL with prevention: tighter specs, better supplier qualification, in-process controls, and DUPRO. Use CAPA/8D after issues.
