AQL inspection explained: sample sizes, defect limits and a QC checklist

Write the defect list for your own product. A generic list misses the problem that matters most for your goods, such as a lid that must seal or a print color that has to match your brand.

Under general inspection level II (the most common setting) the lot size gives a code letter, and the code letter gives the sample size. The table shows common lot sizes for small and mid-sized orders.

Read it like this. For a lot of 1,000 units the inspector pulls 80 at random. With 5 major defects or fewer the batch passes on majors. At 6 or more it fails. Minor defects are counted separately against their own limit, and one critical defect fails the lot.

The sample should come from cartons spread across the whole lot. Units from the top of the first pallet are the ones most likely to have been checked already by the factory.

The inspection level sets how big the sample is for each lot size. General level II is the default and the one most inspection companies quote. Level I uses a smaller sample and suits cheap, simple goods from a supplier you already trust. Level III uses a bigger sample for goods where a miss is expensive.

Special levels S-1 to S-4 use very small samples. They are meant for tests that destroy the unit or take a long time, such as a drop test or a wash test.

• Critical defects: 0. One critical defect fails the batch.
• Major defects: 2.5 for most consumer goods, 1.5 for higher-value items.
• Minor defects: 4.0 for most goods.

A lower AQL number is stricter. AQL 1.5 allows fewer defects in the same sample than AQL 2.5 does.

Stricter limits mean more failed batches and more re-inspections. Set them to match what a return costs you. A $2 accessory and a $60 appliance should not use the same limits.

• Before production: check raw materials and the first units off the line. Useful for custom goods and new suppliers.
• During production: check once part of the order is made, early enough to fix a problem in the rest.
• Pre-shipment: the standard check, done when production is finished and most cartons are packed. Pay the balance after you read the report.
• Container loading: count the cartons and watch them go into the container. Useful if you have had short shipments before.

For 1688 orders the goods usually come to our partner warehouse first. We open and count them there and photograph them against the listing before anything ships. When a factory order needs a full AQL inspection on site, we arrange it and send you the report.

An inspector can only check against what you give them. Send these before the inspection date:

• The approved sample, or clear photos of it from every side.
• The spec sheet with materials, sizes and tolerances.
• Your defect list, with the class of each defect.
• Carton marks, barcode files and label artwork.
• Any function test you want, written step by step.

1. Approved sample and written spec: materials, colors, sizes and tolerances.
2. Quantity check against the packing list and invoice.
3. Visual check of the sampled units against the approved sample.
4. Function tests where they apply, such as switches, zips or closures.
5. Measurements of key dimensions.
6. Packaging, inner packs, carton marks and barcodes.
7. Labels and warnings required in your market.
8. Photos of everything above, attached to the report.

A failed report is where the negotiation starts. Don't pay the balance yet. These are the usual options:

• Ask the factory to sort every unit and rework or replace the bad ones, then inspect again.
• Accept the batch with a discount, if the defects are minor and you can live with them.
• Refuse the batch when critical defects show up or rework cannot fix the cause.
• Agree up front who pays for a re-inspection. Many buyers write into the order that the supplier pays if the first inspection fails.

All of this depends on still holding money. A buyer who paid in full before the inspection has little left to bargain with.

AQL sampling checks workmanship and appearance against your spec. It does not prove the product is safe or legal to sell in your market. Lab tests for materials, chemicals or electrical safety are a separate job for an accredited lab.

A passed report is also no promise that every unit is good. It means the defects in the sample stayed under your limits. If our arrival check misses a problem it should have caught, that is on us. We replace or refund the affected units.