What AQL Actually Measures
The Acceptable Quality Limit is not a claim that a product will have zero defects. It is the maximum defect rate in a sample that is still treated as an acceptable outcome for the lot as a whole. A tighter AQL means fewer defects are tolerated before the lot is rejected; a looser AQL tolerates more.
Sample size itself is drawn from standardized tables in ANSI/ASQ Z1.4, based on the lot size and the chosen inspection level, most commonly General Inspection Level II as the default. A larger lot draws a proportionally larger sample, but not a fixed percentage of the total, which is a common misconception among first-time importers reading an inspection report.
- AQL sets a defect-rate threshold, not a promise of zero defects
- Sample size comes from standardized tables, not a fixed percentage of the lot
- General Inspection Level II is commonly used as the default level
- ANSI/ASQ Z1.4 is internationally equivalent to ISO 2859-1
Critical, Major and Minor Defects
Not every defect carries the same weight, so AQL sampling classifies defects into three tiers, each with its own threshold. A commonly used default sets critical defects at an AQL of 0, meaning none are tolerated, major defects at 2.5, and minor defects at 4.0, though buyers can request different levels to match their own risk tolerance.
A critical defect is one that could cause harm or make a product unsafe or unusable, such as a structural fault in a vanity cabinet. A major defect would likely be noticed by an end user and affect usability or salability, such as a visible finish flaw. A minor defect is a small imperfection unlikely to affect function or a typical buyer's decision to accept the product.
- Critical: commonly AQL 0, no tolerance, safety or basic function affected
- Major: commonly AQL 2.5, likely to affect usability or salability
- Minor: commonly AQL 4.0, small imperfections unlikely to affect function
- These are common defaults; buyers can request tighter or looser levels
When Inspections Happen
Inspection is not a single event tied only to the finished, packed order. A pre-production inspection (PPI) checks raw materials and components before manufacturing begins. A during-production inspection (DPI), sometimes called DUPRO, checks a partially completed run, catching issues while they can still be corrected economically. A pre-shipment inspection (PSI) is the most common, checking a completed, packed order against the AQL standard agreed before shipment. A container loading check (CLC) confirms the correct, undamaged goods are actually loaded into the container being shipped.
Requesting the inspection type that matches the actual risk in an order, rather than defaulting to a pre-shipment inspection alone, catches different classes of problems at the point they are still cheapest to fix.
