AQL inspection levels explained for garment orders

AQL stands for Acceptable Quality Limit. It is a sampling method, not a promise that a lot is defect free. You inspect a random sample from the lot, count defects, and compare the count with a pre-agreed accept or reject number. Most garment buyers base their plans on the ISO 2859-1 style of sampling tables.

The three things that set a plan

1. Lot size. The total number of pieces offered for inspection, usually per style, colour or PO as agreed.
2. Inspection level. This decides how large a sample is for a given lot size.
3. AQL value. The defect rate you are willing to tolerate, set separately for each defect class.

Inspection levels

• General level II is the everyday default and the one most buyers name unless they say otherwise.
• General level I uses a smaller sample. It is used where risk is low or the supplier has a strong record.
• General level III uses a larger sample. It is chosen for high-risk styles or suppliers under watch.
• Special levels (S-1 to S-4) give very small samples. They suit destructive or expensive tests, not routine garment checks.

The lot size and level together give a code letter, and the code letter gives the sample size. A larger lot does not need a proportionally larger sample, which is why sampling is cheap compared with checking every piece.

A worked example

This is an illustration using commonly published table values. Always confirm against the table your buyer specifies.

Suppose a lot of 5,000 pieces is inspected at general level II. That normally gives a sample of 200 pieces. With an AQL of 2.5 for major defects, the plan allows up to 10 major defects to pass and 11 to fail. With an AQL of 4.0 for minor defects, the figures are typically 14 to pass and 15 to fail. Critical defects are almost always set at zero tolerance.

How the decision works

• Count critical, major and minor defects separately in the sample.
• Compare each count with its own accept number.
• If any class exceeds its limit, the lot fails, even if the other classes are fine.
• Defective pieces found in the sample still have to be reworked or replaced. Passing does not clean the lot.

For how defects are sorted into classes, see defect classification.

Common mistakes

• Non-random sampling. Pulling pieces from the top of the carton, or only from cartons the packing team has opened, hides problems in the middle of the lot.
• Mixing lots. Different colours, wash lots or sizes are inspected as one lot, which dilutes the result.
• Inspecting before the lot is ready. The usual rule is that goods are at least 80 percent packed, or whatever the buyer states, so the sample represents the finished shipment.
• Treating AQL as the quality target. An AQL of 2.5 means a lot with a few percent major defects can pass. Factories aiming for that number will ship products that buyers' customers notice. Internal targets should sit well below the buyer's limit.
• Ignoring measurement and function. Size measurement, fit, and functional checks on zips and buttons usually have their own sample counts and tolerances outside the visual AQL table.
• Re-inspecting until it passes. A failed lot should be sorted and reworked first, then re-presented, with the reasons recorded.

Practical advice for factories

Run your own AQL check before the buyer's inspector arrives, using the same table and the same random selection method. If your internal inspection finds the lot is near the reject number, fix the problem first. Track which defect types consume most of your allowance, because that tells you where inline control is weakest.

A short rule worth remembering: AQL controls the risk of shipping a bad lot, it does not remove it. A good inspection plan combines sampling at the end with checks during production, which is why it should sit alongside inline, end-line and final inspection.