Open any pre-shipment inspection report from China and you will find the same line: “General Inspection Level II.” It is the default in the vast majority of commercial inspections worldwide — and most buyers who agree to it have no idea what it actually buys them: how many units get checked, how that number is set, and when a different level would be smarter.
This is the companion to our AQL sampling guide. That article explains the whole system; this one zooms in on the level itself.
What an inspection level is
In the ISO 2859-1 / ANSI/ASQ Z1.4 system, the inspection level is one of the two inputs that set your sample size. The other is the lot size. Together they produce a code letter, and the code letter produces the sample size.
There are seven levels in the standard:
- General levels I, II, and III — for ordinary visual and functional checks.
- Special levels S-1, S-2, S-3, and S-4 — for destructive or expensive tests, where you can only afford to test a handful of units.
General Inspection Level II is the default unless your contract says otherwise. Level I uses smaller samples (cheaper, less discrimination between good and bad lots) and Level III uses larger ones (more discrimination, higher inspection cost). The special levels give very small samples and are used, for example, when the test destroys the unit or requires lab analysis.
Level II sample sizes at a glance
At General Inspection Level II, single sampling, normal inspection, the lot size maps to the sample size like this:
- Lot 2–8: code A, sample 2
- Lot 9–15: code B, sample 3
- Lot 16–25: code C, sample 5
- Lot 26–50: code D, sample 8
- Lot 51–90: code E, sample 13
- Lot 91–150: code F, sample 20
- Lot 151–280: code G, sample 32
- Lot 281–500: code H, sample 50
- Lot 501–1,200: code J, sample 80
- Lot 1,201–3,200: code K, sample 125
- Lot 3,201–10,000: code L, sample 200
- Lot 10,001–35,000: code M, sample 315
- Lot 35,001–150,000: code N, sample 500
- Lot 150,001–500,000: code P, sample 800
- Lot 500,001 and over: code Q, sample 1,250
Two things worth noticing. First, the sample grows much more slowly than the lot: a 500-unit order gets 50 units checked (10%), while a 10,000-unit order gets 200 checked (2%). Second, the sample size is set by the lot-size band, not by preference — if your order is 3,500 units or 9,500 units, the inspector pulls the same 200 units either way.
If the computed sample size equals or exceeds the lot size, the standard calls for 100% inspection instead of sampling — relevant only for very small orders.
Level II in practice: three worked examples
A 500-unit first order. Lot 281–500 at Level II is code H: 50 units sampled. At the usual Critical 0 / Major 2.5 / Minor 4.0, the accept/reject numbers are Major Ac 3 / Re 4 and Minor Ac 5 / Re 6. Three or fewer major defects passes; four fails. On a small first order, that is a meaningful check — 10% of the lot, with a tight threshold.
A 5,000-unit repeat order. Lot 3,201–10,000 is code L: 200 units sampled. Major Ac 10 / Re 11, Minor Ac 14 / Re 15. This is the textbook case — the one your inspector will quote from memory.
A 20,000-unit order. Lot 10,001–35,000 is code M: 315 units sampled. Major Ac 14 / Re 15, Minor Ac 21 / Re 22. The sample is bigger, but it is still only about 1.6% of the lot — which is why the accept numbers, not the sample percentage, are what you should look at.
When to use Level I or Level III instead
Level I is the right call when inspection cost is high relative to the cost of a defect: cheap, simple products where a bad unit costs you almost nothing, or when you are re-inspecting a lot from a supplier with a long clean record. You accept less discrimination in exchange for a smaller bill.
Level III is the right call when discrimination matters more than the inspection fee: expensive products, safety-related goods, a new supplier on a first large order, or a product category where a defect reaches the customer as a return or a chargeback. The sample roughly doubles versus Level II at the same lot size, and the inspector’s fee rises with it — but so does your chance of catching a bad lot.
Special levels S-1 to S-4 are for tests you cannot run on hundreds of units: drop tests, waterproof tests, lab analysis, anything destructive. You might run the general visual and function checks at Level II and the destructive tests at S-2 on the same lot. Write both levels into the order so the inspector plans for both.
The common mistake is letting the factory choose the level. A factory that suggests Level I “to save you money” on a first order is usually saving itself from scrutiny. For a first order with a new factory, Level II is the floor, not the ceiling.
How to write Level II into your order
One line, in every purchase order:
Inspection per ISO 2859-1 (ANSI/ASQ Z1.4), General Inspection Level II, single sampling, normal inspection. Critical AQL 0, Major AQL 2.5, Minor AQL 4.0.
If you want a different level for a specific test, add it explicitly: “Destructive drop test at Special Level S-2, 5 units, zero failures allowed.” Vague instructions produce vague inspections.
And remember the switching rules: you start at normal inspection, move to tightened inspection after repeated failures, and earn reduced inspection only after a long run of passes. A supplier who asks for reduced inspection on a first order has the sequence backwards.
Sources
- IndexFox, “AQL Sampling Explained | How to Read an Inspection Report (ISO 2859-1)” — https://www.indexfox.com/insights/sourcing-guides/aql-sampling-explained/
- AQM BD, “AQL Calculator | Sample Size & ISO 2859-1 Tool” — https://aqmbd.com/quality-control/aql-calculator.php
- SDF Ltd, “AQL Calculator — Free ISO 2859-1 Sample Size Tool” — https://sdfltd.com/tools/aql-calculator/
- NR Tech Studio, “AQL Calculator: Sampling Plans per ANSI/ASQ Z1.4” — https://www.nrtechstudio.com/tools/aql-calculator/