Agreeing an AQL with your supplier: what buyers usually settle before production

This article describes common industry practice, not official rules.

If a buyer and a supplier agree on an AQL in a casual message and leave the rest for later, the inspection result can become the subject of an argument after the goods are packed. A common approach is to settle the points below before production starts and write them into the purchase order or contract. The list covers the sampling standard, the inspection level, the AQL for each defect class, the defect list, the way defects are counted, the lot, who books the inspection, and what happens to a lot that does not pass.

Name the sampling standard and its edition

The contract usually names the sampling standard and the edition the inspection follows. A standard can appear in more than one edition, and later editions can differ in wording or tables. If the contract names only a standard, the buyer and the supplier may end up reading different tables. Writing the edition down lets the inspector work from the same sampling table that the parties checked.

Set the inspection level

The inspection level decides how large a sample is drawn from a lot of a given size. A stricter level usually means a larger sample, which gives more chance of finding a problem in the lot. A lower level draws fewer units and takes less time to carry out. A larger sample can make sense when the product is complex or when a missed defect would be costly for the buyer. The contract should state the level in terms the inspector can check against the sampling table, rather than leave the choice until the day of the inspection.

Give each defect class its own AQL

When the buyer sorts defects into classes, such as critical, major and minor, a common approach is to set a separate AQL for each class. The class with the more serious effect on safety or use is commonly given a stricter limit than the class with a cosmetic effect. Keeping the limits apart also makes a later dispute easier to read, because the report shows which class caused a failure. A combined AQL for the whole product hides that information.

Agree on the defect list for this product

The defect list says what counts as a defect in each class for this product. A line such as "stitching is poor" leaves the inspector to decide what poor means, and a supplier's quality staff and an inspector can read the same unit differently. A common approach is to attach photos marked with the class of each defect, or an approved reference sample that both sides keep. Dimensions and weight limits belong in the specification, with the tolerance written next to each measurement. Where a safety or certification point could matter, whether a legal or certification requirement applies is for the relevant authority, an accredited laboratory or a qualified adviser to confirm.

Decide whether defective units or defects are counted

Sampling can count defective units, meaning units with at least one defect, or it can count each defect found. A unit that shows a few defects counts once under the first method and adds to the total under the second. The two methods can give different results on the same lot, so the contract should name the method in words.

Define the lot for this order

The lot is the batch the sample is drawn from, and the result applies to that batch. For an order, the lot can be the whole order, each shipment, or each style or colour, depending on how the goods are packed and released. Setting the lot in the contract matters because a sample drawn from a mixed group of colours says little about a colour that was not sampled.

Settle who books the inspection, when, and who gets the report

The contract can name who books the third-party inspection company, when the inspection takes place, and who carries its cost as agreed. A common timing is a stage in production, such as after packing and before loading. The report usually goes to the buyer and the supplier together, and it should show the sample size, the defects found in each class and the decision on the lot.

Plan what happens if a lot does not pass

When a lot does not pass, the usual options are a re-inspection after rework, sorting that removes the defective units and offers the rest again, or rejection of the lot. The contract should say which option applies, who books the re-inspection, and who bears the cost of rework or sorting. Leaving these points open often turns a technical result into a commercial dispute, because each side then argues from its own reading of the report.

Keep the agreed points in writing

Points that are only discussed are easy to remember differently later. A common approach is to write the following points into the purchase order or contract:

• the sampling standard named in the contract and its edition
• the inspection level
• the AQL for each defect class
• the defect list, with photos or an approved reference sample
• whether defective units or defects are counted
• what the lot is for this order
• who books the inspection, when it takes place and who receives the report
• what happens to a lot that does not pass, and who bears the cost

The calculator turns the agreed lot size, inspection level and AQL into a sampling plan, so each side can check the same plan against the contract.

A passed lot is not a guarantee

The AQL is a sampling limit that the parties use to decide on a lot. It is not permission to ship defective goods. A lot that passes can still contain defective units, because the sample covers only part of the lot. The contract wording should say this plainly, so that a pass is not read as a promise that the whole lot is free of defects.

Can the agreed AQL change after production starts?

It can, if the buyer and the supplier agree to the change in writing before the inspection takes place. A change made after the goods are packed is harder to check, because the inspector works from the version of the contract that applied when the sample was drawn.