What is the difference between AQL 2.5 and 4.0?

AQL 2.5 is the standard limit for major defects — 2.5% of the lot may be defective before rejection. AQL 4.0 covers minor defects — 4.0% tolerance. Critical defects always use AQL 0.

How is sample size chosen?

By lot size and inspection level. Level II (general) is the default; for a lot of 3,200 pieces the sample is 125 units at S-2 / 200 units at Level II.

What happens if the lot fails?

The buyer decides: 100% re-inspection, rework, or rejection. Never ship without a signed CAP (Corrective Action Plan) — future audits reference it.

AQL Sampling for Apparel: 2.5 and 4.0 Explained with a Real Inspection

AQL 2.5 vs 4.0, ANSI/ASQ Z1.4 tables, and how a QA inspector reads a lot without over-rejecting — with a step-by-step example.

What AQL actually means

AQL (Acceptable Quality Limit) is the worst-case percentage of defective units the buyer will accept as a process average. It is not a target — it is the trip wire. A factory averaging 1% defective easily passes AQL 2.5; one averaging 2.4% is one bad shift away from a failed shipment.

The three defect classes

Class	Definition	Typical AQL
Critical	Safety or regulatory — sharp point, needle fragment, missing CPSIA label	0
Major	Functional or appearance defect noticeable to the end user — broken stitch, misaligned pocket, wrong shade	2.5
Minor	Slight deviation that does not affect use — loose thread ends, minor puckering	4.0

Buyer tech packs override these — always confirm.

Choosing sample size (ANSI/ASQ Z1.4)

Single sampling plan, Inspection Level II, Normal:

Lot size	Sample	Accept (2.5)	Reject (2.5)	Accept (4.0)	Reject (4.0)
501-1200	80	5	6	7	8
1201-3200	125	7	8	10	11
3201-10000	200	10	11	14	15
10001-35000	315	14	15	21	22

Example: 5,000-piece PO. Draw 200 units at random across every carton and every color. Passing at AQL 2.5 means no more than 10 major defects across the 200.

Running the inspection — 8-step protocol

Verify the lot is 100% packed and cartons are randomly selected across the shipment.
Audit shipping marks on 10% of cartons.
Measurement check on 8 pieces per size — a single out-of-spec unit is a major.
Workmanship inspection on the full sample under 1,000 lux daylight-balanced light.
Color / shade grouping against approved swatch under D65.
Fit / spec check on-body (or on dress form) for 3 pieces per size.
Barcode and packaging verification.
Log defect codes against the buyer's master list — never freestyle categories.

Common mistakes that fail audits

Sample drawn only from top cartons — invalidates randomness.
Inspector counts multiple defects on one garment as one — each defect counts.
Passing on tolerance (e.g. "one over accept") — the buyer's standard is binary.
Inspection lighting below 1,000 lux — shade defects go undetected.