AQL · Z1.4

AQL sampling plan calculator

Set the inspection sample before the inspector arrives at the floor.

Tell a third-party inspector "check some units" and you get an arbitrary sample that proves nothing and holds up in no dispute. The ANSI Z1.4 / ISO 2859-1 plan fixes the sample size and the accept/reject threshold to the lot size in advance, so a passed lot is defensible and a failed one is actionable, not a judgement call.

Type the lot size and the AQL and the tool returns the ANSI Z1.4 / ISO 2859-1 Level II Normal Inspection sample size and the accept/reject thresholds to brief the inspector with.

Last updated 2026-05-09. Math runs in your browser, no data leaves your computer.

The total units in the production lot, not the order. The standard scales the sample to the lot, so use the actual batch count being inspected.

How strict the inspection is. Use 2.5 for general visual and packaging defects, 1.0 or tighter for critical attributes like purity, 4.0 only for cosmetic ones.

General guidance only. Verify against the cited primary sources before you commit to a shipment, declaration, or contract.

AQL Z1.4 in chemical-trade audits

ANSI Z1.4 (formerly MIL-STD-105E) is the global standard for sample-based lot acceptance inspection. ISO 2859-1 mirrors it word-for-word. Buyers use the standard to inspect a manageable sample (32 to 200 units typically) instead of every unit in a lot, accepting or rejecting the whole lot based on the defects found in the sample.

Level II is the default inspection level for ongoing buyer-supplier relationships; it provides a reasonable balance between inspection cost and consumer risk. AQL 2.5 is the most-used acceptance level for chemical product attributes (visual defects, packaging integrity, label correctness). For critical attributes (purity, heavy metals, regulatory parameters), AQL 1.0 or even tighter (0.65, 0.40) is the right level; for non-critical (cosmetic), AQL 4.0 or 6.5 is acceptable.

The tool returns the code letter, sample size, and accept-reject thresholds for the chosen lot size and AQL. Apply the inspection plan to the lot, count defects in the sample, compare against the Accept / Reject thresholds for the lot decision.

A worked example

The booking. You order 1,000 cartons and tell the third-party inspector to "check a good number of them". The inspector opens 20, finds 1 defect, and passes the lot.

The failure. The lot is bad. With no agreed plan, that 20-unit check has no statistical meaning, and when the cargo lands with a 3% defect rate you have no standing to reject it, because nothing defined what "pass" was. An arbitrary sample proves nothing and holds up in no dispute.

The fix. Set the plan first. For a 1,000-unit lot at AQL 2.5, Z1.4 Level II calls for a sample of 80, accept on 5 defects, reject on 6. Brief the inspector with those exact numbers. Now a pass is defensible and a fail is actionable, and the supplier knows the bar before production starts.

Running the full pre-shipment audit, not just the count? The supplier audit checklist generator builds the inspection sheet at /tools/sales-and-ops/supplier-audit-checklist-generator.

Tracking the samples that set the spec in the first place? The sample tracking log is at /tools/sales-and-ops/sample-tracking-log.

Frequently asked

What is AQL?

Acceptable Quality Limit. The maximum percentage of defective units in a lot that the buyer will accept on average across many lots. AQL 1.0 = strictest (1% defective accepted on average); AQL 2.5 = standard for chemical and consumer goods; AQL 4.0 = lenient.

What is normal inspection level II?

The default ANSI Z1.4 inspection level. Higher levels (III, IV) increase sample size and reject more aggressively; lower levels (I) reduce sample size for trusted-supplier histories. Most buyer audits start at level II.

How do I read the result?

Inspect the sample size given. Count defects in the sample. If defects <= Accept (Ac), accept the lot. If defects >= Reject (Re), reject the lot. The numbers in between are not possible (Ac + 1 = Re).

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