G03 AQL

Your inspection report says "passed." Your ops team says quality is handled. But many teams ordering inspections cannot explain the math behind accept and reject. That gap shows up in your return rate.

AQL 2.5 does not mean 2.5% defects allowed.

Here is what it means: at a sample size of 125 units, AQL 2.5 allows up to 7 defects before rejection. That is 5.6% of the sample, more than double 2.5%.

AQL is a sampling system, not a defect rate ceiling.

What AQL actually is:

AQL (Acceptable Quality Limit) is defined by ISO 2859-1. It is an acceptance sampling system that tells you how many units to inspect and how many defects trigger a pass or fail. The number represents the worst tolerable process average across a continuing series of lots, not a guarantee for any single shipment.

Inspection levels determine sample size:

General Inspection Level II is the industry default. Level I uses smaller samples with lower cost but less statistical confidence. Level III uses larger samples with higher confidence but higher cost. Most buyers stay on Level II unless they have a specific reason to change.

Defects are not equal:

This is where most inspection specs fail. You cannot apply one AQL to all defects. Industry standard practice maps AQL values to defect severity like this:

Critical defects (safety hazards, regulatory failures): AQL 0. Zero acceptance. One critical defect fails the lot (Ac 0 / Re 1).

Major defects (function, performance, usability): AQL 2.5 is common. Stricter programs use AQL 1.0 or 1.5.

Minor defects (cosmetic issues that do not affect use): AQL 4.0 is typical.

A typical inspection spec reads: "General Inspection Level II: Critical AQL 0, Major AQL 2.5, Minor AQL 4.0."

If your spec says only "AQL 2.5" without breaking down defect classes, the inspection firm applies their default classification. Their defaults may not match your risk tolerance or your customer expectations.

AQL numbers do not guarantee quality. Your defect classification does.

Practical checklist:

• Write a defect classification list before production. Define critical, major, and minor with photos, measurements, and examples
• Specify AQL for each defect category in your inspection criteria. A common baseline is Critical 0, Major 2.5, Minor 4.0
• State your inspection level (defines the sample size). Level II is standard
• Clarify how defects are counted: defective units versus multiple defects on one unit. This matters when the same unit has several issues.
• Always review raw inspection data, not just pass or fail

Forward this to your ops lead. If they already know it, good. If they do not, you just prevented your next sea container of returns.

AQL cheat sheet

This cheat sheet is the fast reference for writing and reading AQL-based inspection specs. It summarizes what inspection levels change (sample size), how AQL maps to Critical/Major/Minor defect severity, and includes a few worked examples that show why “AQL 2.5” is not “2.5% defects.” Use it

Yury Galtykhin | Fractional COO and Hardware Startup ConsultingYury Galtykhin

AQL Calculator

What this calculator does This calculator helps you interpret an inspection report that uses AQL sampling. It estimates: * The sample size (n) from lot size and inspection level * The accept/reject thresholds (Ac/Re) for Critical, Major, and Minor defects Then you can check whether the reported defect counts should

Yury Galtykhin | Fractional COO and Hardware Startup ConsultingYury Galtykhin