The short version
- An inspection should follow a written plan agreed before production ends: how many units are checked, what counts as a defect, and how many defects are allowed.
- The usual method is AQL sampling under ISO 2859-1 (its American counterpart is ANSI/ASQ Z1.4).
- A common starting point is General Inspection Level II with limits of 0 for critical, 2.5 for major and 4.0 for minor defects. You can agree other numbers.
- On small batches we can check every unit; on larger orders we check a sample under a plan agreed with you.
What AQL means
AQL stands for Acceptance Quality Limit. In ISO 2859-1 it is the worst quality level that is still considered acceptable as a process average when lots are inspected one after another. In day-to-day trade it works as the agreed pass-or-fail limit: it says how many defects the sample may contain before the lot is rejected.
ISO 2859-1 sets out sampling schemes for lot-by-lot inspection by attributes. ANSI/ASQ Z1.4 is the American counterpart, and buyers and inspection companies use the two names interchangeably.
An AQL sample is a statistical check, not a guarantee. A lot that passes can still contain some defective units. The AQL tells you how much risk you have agreed to accept. If you want less risk, ask for a stricter AQL, a higher inspection level, or both.
How the sample size is chosen
There are three steps:
- Lot size and inspection level give a code letter. The lot size is the number of units being inspected together. General Inspection Level II is the usual default. Level I uses a smaller sample and Level III a larger one. Special levels S-1 to S-4 exist for cases where small samples are acceptable, such as destructive or costly tests.
- The code letter gives the sample size.
- The sample size and the AQL give two numbers: the accept number (Ac), the highest number of defects that still passes, and the reject number (Re), the number at which the lot fails.
The sample should be drawn at random from the whole lot, across cartons and pallets, not from the top of one pile.
Defect classes: critical, major and minor
Each defect found is put in one class, and each class has its own AQL.
| Class | Meaning | Examples on auto parts | Common AQL |
|---|---|---|---|
| Critical | Could hurt the user, or breaks a safety rule or law. | A crack in a load-bearing part or weld; exposed live parts in an electrical product. | 0 (none accepted) |
| Major | Likely to make the product fail, be unusable or not match the order. | A dimension outside tolerance so the part will not fit; wrong material or finish; a missing component; a failed function check. | 2.5 |
| Minor | Departs from the specification but does not affect use or sale much. | A small scratch or paint blemish; a slightly misaligned label; a loose packaging insert. | 4.0 |
These values are common starting points in trade, not requirements of the standard. They can be set by the buyer: stricter limits, such as 1.5 for major defects, are often used for higher-value or safety-related parts. Put the classes and limits in the purchase order or contract and share them with us, so the inspection checklist uses the same definitions.
Simplified AQL example: General Level II, normal inspection
The table below shows single sampling for normal inspection at General Inspection Level II, for lot sizes from 151 to 35,000 units. It is a simplified extract to show how the method works.
| Lot size (units) | Code letter | Sample size | AQL 2.5 accept / reject | AQL 4.0 accept / reject |
|---|---|---|---|---|
| 151 – 280 | G | 32 | 2 / 3 | 3 / 4 |
| 281 – 500 | H | 50 | 3 / 4 | 5 / 6 |
| 501 – 1,200 | J | 80 | 5 / 6 | 7 / 8 |
| 1,201 – 3,200 | K | 125 | 7 / 8 | 10 / 11 |
| 3,201 – 10,000 | L | 200 | 10 / 11 | 14 / 15 |
| 10,001 – 35,000 | M | 315 | 14 / 15 | 21 / 22 |
Smaller and larger lots follow additional rules in the standard (arrows in the tables), and the sample size can differ between AQL values. Check the full tables in ISO 2859-1 or ANSI/ASQ Z1.4 before you write numbers into a contract.
Worked example. A lot of 5,000 units falls in the 3,201 – 10,000 band, code letter L, so 200 units are checked. For major defects at AQL 2.5 the lot passes with 10 or fewer and fails at 11. For minor defects at AQL 4.0 it passes with 14 or fewer and fails at 15. For critical defects the limit is 0, so a single critical defect fails the lot.
What we check on auto parts
The checklist is built from your drawing, your approved sample and your purchase order. These are the usual areas:
| Area | Examples |
|---|---|
| Dimensions and fit | Measured against the drawing or approved sample. On wheels, for example, center bore, offset and bolt pattern; on brackets, hole positions. |
| Appearance and finish | Casting marks, paint, varnish or plating, scratches and color match against the approved sample. |
| Markings and labels | Part numbers, specification stamps, labels in the agreed language and barcodes where they apply. |
| Packaging | Carton marking, inner protection, quantity per carton and how the goods are loaded on pallets or in the container. |
| Function checks | Simple checks that can be done on site, such as a balance check on wheels or switching on lighting parts. |
For each inspection you receive a photo and video report, with the goods compared against your original sample and specifications. You approve what you see before anything ships.
What an AQL inspection does not do
- It does not make the rest of the lot defect-free (see above).
- It is not a laboratory test and does not certify that a product meets a regulation or a standard. For lab testing or certificates, use an accredited laboratory or a large inspection company (see how to choose a provider).
- It does not tell you whether the supplier is a real factory. That is the job of a factory verification, which is best done before you pay a deposit.
How this fits with our services
Our pre-shipment inspection service applies the method above at your supplier's factory before the goods are loaded. It is priced per man-day, and current prices are on our services and pricing section. Before that, a factory verification checks that the factory is real and able to make your order.
We have no financial reason to let goods pass: prices are fixed and we take no commission from factories (see our impartiality statement). To see what a report looks like, open the sample report.
Frequently asked questions
What is AQL in simple terms?
AQL (Acceptance Quality Limit) is the agreed limit on defects in an inspection sample. If the sample has no more defects than the accept number for that class, the lot passes; if it has the reject number or more, the lot fails.
Which standard is AQL based on?
The usual reference is ISO 2859-1, sampling procedures for inspection by attributes. Its American counterpart is ANSI/ASQ Z1.4, and the two are treated as equivalent in everyday trade.
What does General Inspection Level II mean?
It is the default inspection level in the standard. Level I uses a smaller sample and Level III a larger one, so the level sets how much evidence the inspector collects for a given lot size.
Can I set my own AQL values?
Yes. Critical 0, major 2.5 and minor 4.0 are common starting points, not a rule. Buyers often use stricter limits for higher-value or safety-related parts. Agree them in writing with your supplier before production ends.
Do you check every unit or only a sample?
On small batches we can check every unit. On larger orders we check a sample under a plan agreed with you in advance.
Does a passed AQL inspection mean the whole lot is defect-free?
No. AQL sampling is a statistical check. A lot can pass and still contain some defective units; the AQL describes the level of risk you have agreed to accept.
Agree the inspection plan before you pay
Tell us the product, the order size and the limits you want, and we will build the checklist with you. If you are not sure the factory is real yet, start with a remote check.