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The short version
- AQL means acceptance quality limit (often called acceptable quality limit or level): the worst defect rate you will still accept, used to pass or fail a whole order from a random sample.
- The sampling tables come from ISO 2859-1 and its US twin ANSI/ASQ Z1.4. General Level II is the default for consumer goods.
- The common choice is 0 for critical, 2.5 for major and 4.0 for minor defects.
- Example: a lot of 5,000 units at Level II is code letter L, so the inspector checks 200 units. At AQL 2.5 the lot passes with up to 10 major defects; at 4.0, up to 14 minor ones.
- Book the pre-shipment inspection when at least 80% of the order is finished and packing has started, and pay the balance only after the report passes.
- Our pick: QIMA. It samples to ANSI/ASQ Z1.4-2008 and sends the report the same day as the inspection.
What does AQL mean?
AQL stands for acceptance quality limit: the highest percentage of defective units that you still treat as acceptable on average. Instead of checking every unit, an inspector pulls a random sample sized by the AQL tables, counts the defects and passes or fails the whole lot against two numbers: accept (Ac) and reject (Re). Inspection companies and buyers often say “acceptable quality limit” or “acceptable quality level”; ISO's official term is acceptance quality limit. When a supplier or inspector writes “AQL 2.5”, they mean the plan is built around a 2.5% defect level for that class of defect.
Which standards define AQL sampling?
Two standards with the same tables. ISO 2859-1 is the international one; its third edition was published on January 22, 2026 and replaces the 1999 edition. ANSI/ASQ Z1.4 is the American national standard; ASQ describes it as a direct descendant of the old military standard MIL-STD-105E. QIMA states that its inspectors sample to ANSI/ASQ Z1.4-2008. The table values on this page are the long-standing ones that inspection companies publish; if your contract names the 2026 edition of ISO 2859-1, ask your inspector to confirm the plan before the visit.
What are AQL inspection levels?
The inspection level sets how big the sample is for a given lot size. There are three general levels and four special ones.
| Level | Sample size | Used for |
|---|---|---|
| General I | About 40% of Level II | Products with less strict requirements |
| General II | The reference size | The default; the most common plan for consumer products |
| General III | About 160% of Level II | Products with stricter requirements |
| Special S-1 to S-4 | Very small samples | Checks that only make sense on a few units, such as specific on-site tests |
Level shares from the China2West ISO 2859-1 chart; uses from HQTS.
How do you read an AQL table?
- Find the code letterLook up your lot size (the total units in the order) in the first table and read the letter under your inspection level.
- Read the sample sizeEach code letter has one sample size: the number of units the inspector picks at random.
- Read Ac and Re for your AQLIn the second table, go to your AQL column. If the defects found are at or below Ac, the lot passes; at Re or above, it fails. In single sampling for normal inspection, Re is always Ac plus one.
| Lot size | Level I | Level II | Level III |
|---|---|---|---|
| 151 to 280 | E: 13 units | G: 32 units | H: 50 units |
| 281 to 500 | F: 20 units | H: 50 units | J: 80 units |
| 501 to 1,200 | G: 32 units | J: 80 units | K: 125 units |
| 1,201 to 3,200 | H: 50 units | K: 125 units | L: 200 units |
| 3,201 to 10,000 | J: 80 units | L: 200 units | M: 315 units |
| 10,001 to 35,000 | K: 125 units | M: 315 units | N: 500 units |
| 35,001 to 150,000 | L: 200 units | N: 500 units | P: 800 units |
Excerpt of the ISO 2859-1 code letter and sample size tables, normal inspection. Code letters from the China2West chart; sample sizes from the QCAdvisor chart.
| Code letter (sample) | AQL 1.5 | AQL 2.5 | AQL 4.0 |
|---|---|---|---|
| J (80 units) | Not shown | Accept 5, reject 6 | Accept 7, reject 8 |
| L (200 units) | Accept 7, reject 8 | Accept 10, reject 11 | Accept 14, reject 15 |
Single sampling, normal inspection. Sources: QIMA (L at 2.5), qualityinspection.org (L at 4.0), Global Sources (L at 1.5), HQTS (J at 2.5 and 4.0).
Which AQL should you choose?
Set one AQL per class of defect and write all three on the purchase order:
| Defect class | What it means | Common AQL | Higher-value goods |
|---|---|---|---|
| Critical | Could harm the user or breaks a safety rule | 0 | 0 |
| Major | The end customer would reject the product | 2.5 | 1.0 / 1.5 |
| Minor | Off spec, but most buyers would still accept it | 4.0 | 2.5 / 4.0 |
Common practice per HQTS and QIMA; higher-value column from V-Trust.
AQL 0 for critical defects means one critical defect in the sample fails the lot. A lower AQL number is stricter: fewer defects are allowed in the same sample.
What does an AQL inspection look like in numbers?
Our worked example: 5,000 insulated water bottles, General Level II, AQL 0 / 2.5 / 4.0.
| Step | Result |
|---|---|
| Lot size 5,000, Level II | Code letter L |
| Sample size | 200 bottles, 4% of the lot |
| Critical, AQL 0 | Any critical defect fails the lot |
| Major, AQL 2.5 | Pass with 10 or fewer, fail at 11 |
| Minor, AQL 4.0 | Pass with 14 or fewer, fail at 15 |
| Found: 0 critical, 9 major, 15 minor | Fail: minor defects hit the reject number |
Illustrative order; the plan values come from the tables above.
The lot fails even though major defects passed, because each class is judged on its own. The usual next step is that the factory sorts or reworks the goods and you book a re-inspection. Now the same plan on a small order: 960 units is code letter J, so the inspector checks 80 units, 8.3% of the lot, and the lot passes with up to 5 major and 7 minor defects. Small orders get a bigger share checked, so AQL inspections pay off even on a first order.
What does a pre-shipment inspection check?
A pre-shipment inspection (PSI) is an on-site check of the finished order, with the sample sized by the AQL tables. QIMA's PSI covers:
- Quantities of semi-finished, finished and packed products.
- Specifications: colors, style and construction, compared with your golden sample.
- Functional tests and a material composition check.
- Workmanship: imperfections and assembly.
- Dimensions and unit weight.
- Packing: export carton dimensions and weights, and shipping marks on the cartons.
When should you book a pre-shipment inspection?
Book it for the day at least 80% of the order is finished and packing has started, which is the line QIMA uses. Earlier than that, the inspector cannot sample the whole lot; later, there is no time left to fix problems before the ship date. Put the inspection in the proforma invoice: the balance is paid only after a passed report.
What is the difference between DPI, PSI and a container loading check?
| Inspection | When | What it catches |
|---|---|---|
| During production (DPI or DUPRO) | When 20% to 80% of production is done | Defects and delays while the line can still change |
| Pre-shipment (PSI) | At least 80% finished, packing started | Final quality of the lot by AQL sampling, before you pay the balance |
| Container loading check (CLC) | While the container or truck is loaded | Quantities loaded, carton details, container condition and the loading process |
Timing and scope from QIMA's DUPRO, PSI and CLC pages.
For a first order with a new factory, the PSI is the one to book. Add a DPI for long production runs or a custom product, and a loading check when you ship a full container. Our guide to factory audits in China covers the audit you do before you place the order.
Send the inspector your AQL levels, your defect list (what counts as critical, major and minor for your product) and a sealed golden sample. Without them, the report cannot say pass or fail on the things you care about.
Who should do your pre-shipment inspection?
Our pick: QIMA. Its inspectors sample to ANSI/ASQ Z1.4-2008, the report arrives the same day the inspection is completed, and it quotes a pre-shipment inspection and a container loading check together. Pricing depends on the product, location and scope, so request a free quote with your lot size and AQL levels from this guide.
Book a pre-shipment inspection with QIMA and get the AQL report before you pay your supplier's balance.
Get a free QIMA quoteThis guide includes an affiliate link. If you book through it, we may earn a commission at no extra cost to you.
Frequently asked questions
What does AQL 2.5 mean?
It means the sampling plan is built around a 2.5% defect level for that defect class, usually major defects. For a sample of 200 units, the lot passes with up to 10 defects and fails at 11.
What does AQL 4.0 mean?
It is the looser level most buyers use for minor defects. For a sample of 200 units, the lot passes with up to 14 minor defects and fails at 15.
How many units are checked in a 1,000 piece order?
At General Level II, a lot of 501 to 1,200 units is code letter J, so the inspector checks 80 units.
Is AQL a percentage of the sample?
No. The pass or fail decision uses the accept and reject numbers in the table for your sample size, not a simple percentage of the units checked.
What is the difference between ISO 2859-1 and ANSI/ASQ Z1.4?
ISO 2859-1 is the international standard and ANSI/ASQ Z1.4 is the American national standard. Both give AQL sampling tables used in pre-shipment inspections.
When is a pre-shipment inspection done?
When at least 80% of the order is finished and packing has started, so the inspector can sample the whole lot and problems can still be fixed before shipping.
This guide is general information. Sampling plans, AQL levels and inspection terms are agreed per order: put them in writing with your supplier and inspector. SuanSupply is not affiliated with ISO or ASQ.