Every drinkware purchase order eventually asks the same question: how many units does the inspector actually open, and how many defects are allowed before the container is rejected? Most buyers answer that question with a number someone told them at a trade show, usually "AQL 2.5" — and most of them do not know that AQL 2.5 is not a number of defects. It is a lookup key into a sampling table. Below is that table, the clause we recommend writing into your purchase order, and how to read a report when one comes back marked "fail".
AQL means Acceptable Quality Limit. Under ISO 2859-1 (identical to ANSI/ASQ Z1.4), the standard behind every SGS, Bureau Veritas and Intertek inspection, an AQL is a process quality level used to look up two numbers in the sampling table: an Accept number (Ac) and a Reject number (Re). The lot passes if the number of defects found in the random sample is at or below Ac. It fails at or above Re. That is the whole mechanism.
The most common misunderstanding in the industry is that AQL 2.5 means "2.5% of the goods may be defective". It does not, and it never did. In a lot of 3,000 units, AQL 2.5 means the inspector opens 125 units and the lot passes with up to 7 major defects in that sample, failing at 8. Read the other way: if your inspector found 7 major defects in 125 units and you had been told the allowance was "2.5%", you would rightly think you had been overcharged for a bad lot.
This is the table to print and paste into your buying file. Find your lot size in the first column, take the sample size, and use the Ac/Re pair for the defect class you have agreed. Source: ISO 2859-1 / ANSI/ASQ Z1.4 Table II-A, General Inspection Level II, normal inspection, single sampling plan.
| Lot size (units) | Code letter | Sample size (n) | AQL 2.5 Ac / Re (major) | AQL 4.0 Ac / Re (minor) | Sample as % of lot |
|---|---|---|---|---|---|
| 2 – 8 | A | 2 | 0 / 1 | 0 / 1 | 100% |
| 9 – 15 | B | 3 | 0 / 1 | 0 / 1 | 20–33% |
| 16 – 25 | C | 5 | 0 / 1 | 0 / 1 | 20–31% |
| 26 – 50 | D | 8 | 0 / 1 | 1 / 2 | 16–31% |
| 51 – 90 | E | 13 | 1 / 2 | 2 / 3 | 14–25% |
| 91 – 150 | F | 20 | 1 / 2 | 3 / 4 | 13–22% |
| 151 – 280 | G | 32 | 2 / 3 | 5 / 6 | 11–21% |
| 281 – 500 | H | 50 | 3 / 4 | 7 / 8 | 10–18% |
| 501 – 1,200 | J | 80 | 5 / 6 | 7 / 8 | 6.7–16% |
| 1,201 – 3,200 | K | 125 | 7 / 8 | 10 / 11 | 3.9–10.4% |
| 3,201 – 10,000 | L | 200 | 10 / 11 | 14 / 15 | 2.0–6.3% |
| 10,001 – 35,000 | M | 315 | 14 / 15 | 21 / 22 | 0.9–3.1% |
| 35,001 – 150,000 | N | 500 | 21 / 22 | 21 / 22 | 0.33–1.4% |
| 150,001 – 500,000 | P | 800 | 21 / 22 | 21 / 22 | 0.16–0.53% |
Two practical notes on reading this table. First, a lot is one model, one production batch, one colour — not one purchase order. If you order five SKUs in one PO, that is normally five lots and five inspections. Second, the sample percentage falls as the lot grows, but the absolute number of units inspected rises. That is why inspection cost for a 30,000-piece order is materially higher than for a 3,000-piece order, and it is why suppliers who quote one flat inspection fee for wildly different volumes are either absorbing it or not inspecting properly.
Lot size 3,000 falls in the 1,201–3,200 row. Code letter K, sample size 125 units, randomly selected from the packed lot. Critical defects (AQL 0, zero acceptance): 0 accepted, 1 rejects the lot. Major defects at AQL 2.5: up to 7 in the sample pass, 8 or more fails. Minor defects at AQL 4.0: up to 10 pass, 11 fails. The inspector also applies tightened inspection if the last three lots passed, which raises the sample size and lowers the Ac numbers; and reduced inspection after a failure streak, which lowers the sample size. Both are automatic under ISO 2859-1 clause 9 and both catch buyers who do not know they are being inspected more strictly than they planned for.
The numbers above only mean something once you and the inspector agree what counts as critical, major and minor. Agreed defect lists are where drinkware inspections most often go wrong, because "scratches" and "seams not vacuum-tight" are interpreted differently on each side. A workable classification for drinkware:
Write these into the inspection brief, not just "AQL 2.5". An inspector working without an agreed defect list will apply their own judgement, and their judgement will be defensible to them and not to you.
Copy this and fill the brackets:
Inspection: Pre-shipment inspection by [SGS / Bureau Veritas / Intertek / TUV] at [factory address], on [date], at [X]% of production and 100% of packing. Sampling per ISO 2859-1 / ANSI/ASQ Z1.4, General Inspection Level II, normal inspection, single sampling plan, using the agreed defect list dated [date]. Critical defects: AQL 0. Major defects: AQL 2.5. Minor defects: AQL 4.0. A lot is [model / colour / batch]. The lot passes if the number of defects in the sample is at or below the Accept number for each class; otherwise the lot is rejected and subject to sorting, rework, replacement or concession. Charges for inspection are borne by the buyer. Any re-inspection after a failure is at the buyer's cost.
Add one line that most buyers forget: who pays for a second inspection if the first fails. Without it, the supplier will usually arrange the rework and the re-inspection at their cost, which quietly weakens the inspection.
A failed AQL lot is not a destroyed container. Under ISO 2859-1 the buyer's options are, in order of preference: rework or sort at the factory (most common for drinkware — replacing a lid or re-welding a base), concession with a price adjustment, replacement of the non-conforming portion, or rejection of the lot. Insist on a written record of what was found, what was done, and a re-inspection on the corrected goods. Re-inspection after 100% sorting is usually cheaper than rejecting a container that is 95% good, and that is almost always the right commercial answer for drinkware.
Inspection is normally charged per inspector-day, typically a few hundred US dollars per day plus travel, and it is added to your production timeline — the inspector needs the goods packed, not in the last hour of production, or you will pay for a second visit. Book the inspection after production but before the container is sealed, and tell the factory in advance that the goods will be inspected, so it is not a surprise that delays loading. At STWADD we hold AQL 2.5 inspection before the container is sealed on every order, and we publish the original third-party test reports for the materials we use — you can read the SGS food-contact report and the STSGZ US food-contact report for the exact products and dates at our certifications page.
We are a factory-backed supply company in Yongkang, Zhejiang: production runs to your specification at audited partner factories that we qualify and work with directly, our own QC team is stationed on the line, and the final check happens before the container is sealed rather than after it has sailed. If you would like the inspection brief drafted for your order, send the model, quantity and destination port and we will send it back with the lot definition and the sampling rows for your quantity filled in. Our OEM and ODM page covers sampling, lead times and inspection, and the 2026 catalogue lists every model with carton data so the inspection can start from a specification rather than from a photograph.
What does AQL 2.5 mean in plain terms? It is the quality level used to look up an accept number and a reject number in the ISO 2859-1 sampling table. For a 3,000-unit lot, the inspector opens 125 units; the lot passes with 7 or fewer major defects and fails at 8. It does not mean 2.5% of the goods may be defective.
How many units do I need inspected for a 10,000-piece order? At General Inspection Level II, a lot of 3,201 to 10,000 units uses code letter L: sample size 200, accept 10 / reject 11 major defects at AQL 2.5, and accept 14 / reject 15 minor defects at AQL 4.0.
Does AQL 2.5 mean the supplier can deliver 2.5% defective goods? No. AQL sets the decision rule for a random sample, not a permitted defect rate in the shipment. The supplier's obligation is the specification; the AQL is how you verify it.
Who pays for a pre-shipment inspection? Normally the buyer, as an inspection cost on top of the production price. Agree it in the purchase order, and also agree who pays for a re-inspection after a failure.
Can I inspect at my own factory? You can send your own inspector or use a third-party agency such as SGS, Bureau Veritas, Intertek or TUV. At STWADD our QC team is on the line before the container is sealed, and we invite third-party inspection before shipment on request.