# AQL calculator: ANSI/ASQ Z1.4 and ISO 2859-1 sampling plans

> Free AQL calculator to ANSI/ASQ Z1.4 and ISO 2859-1: sample size, code letter and accept/reject numbers for critical, major and minor defects, arrows handled.

Source: https://sourcesquid.co/tools/aql-sampling-planner/

Quality tool · free

# AQL sampling planner. How many to check, how many to accept.

An AQL sampling plan tells an inspector how many units to pull from a lot and how many defects of each class the lot can contain and still be accepted. Enter your lot size, inspection level and AQLs, and this planner reads ANSI/ASQ Z1.4 (ISO 2859-1) Tables I and II exactly, arrow rules included, and states the decision rule in plain English.

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Units to check**200**

How this plan protects you

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How it works

## Three steps. One clear answer.

  1. 01

Enter the lot size, keep General Inspection Level II unless you have a reason to change it, and choose normal, tightened or reduced inspection.

  2. 02

Set the AQL for critical, major and minor defects; 0, 2.5 and 4.0 suit most consumer goods.

  3. 03

Read the sample size, the Ac and Re numbers for each class and the plain-English rule, then share it with your inspector or factory.

Method and sources

Table I of ANSI/ASQ Z1.4-2003 (reaffirmed 2018), the successor to MIL-STD-105E, maps the lot size and inspection level to a sample size code letter (A to R). Tables II-A (normal), II-B (tightened) and II-C (reduced) give the sample size and the acceptance (Ac) and rejection (Re) numbers for single sampling. Where the table shows an arrow, the first plan below or above the arrow is used together with that plan's sample size, so classes can end up with different sample sizes. If the sample size equals or exceeds the lot size, every unit is inspected. A critical AQL of 0 means zero acceptance on the code letter's sample (Ac 0, Re 1). ISO 2859-1 uses the same code letters and normal and tightened single plans; its 1999 revision changed some other accept/reject pairs, so for reduced inspection follow the standard your contract names. Acceptance probabilities use the binomial model. Switching: move from normal to tightened when 2 of 5 consecutive lots are not accepted, and back to normal after 5 consecutive lots are accepted on tightened inspection.

  * [ASQ: ANSI/ASQ Z1.4 and Z1.9 sampling standards](https://asq.org/quality-resources/z14-z19)
  * [ISO 2859-1: sampling by attributes indexed by AQL](https://www.iso.org/standard/1141.html)

Results are estimates to support your decisions. For binding figures, ask our team or your customs broker.

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AQL sampling questions

## Straight answers.

Anything else, ask us directly. A principal replies, not a bot.

[anirudh@sourcesquid.co](mailto:anirudh@sourcesquid.co)

### What does AQL 2.5 mean?

AQL 2.5 is the worst process average, 2.5 defective units per 100, that is still considered acceptable over a series of lots. It is not a target: a lot at 2.5% defective is accepted most of the time, and lots well above it are accepted rarely.

### How many units should I inspect for a lot of 3,500?

At General Inspection Level II on normal inspection, a lot of 3,201 to 10,000 units gets code letter L, so you check 200 units. At AQL 2.5 you accept with 10 or fewer major defects; at AQL 4.0, 14 or fewer minor defects.

### What do the arrows in the AQL table mean?

An arrow means there is no plan for that code letter and AQL. Follow the arrow to the first plan below or above it and use that plan's sample size as well as its Ac and Re numbers. That is why major and minor defects can need different sample sizes.

### What AQL should I use for critical, major and minor defects?

Most importers of consumer goods use 0 for critical defects (none accepted), 2.5 for major and 4.0 for minor. Use lower values, such as 1.0 or 1.5 for major, for products where function or safety matter more.

### Is ANSI/ASQ Z1.4 the same as ISO 2859-1?

They share the same origin, MIL-STD-105E, the same code letters and the same normal and tightened single sampling plans. ISO 2859-1 changed a few accept/reject pairs in its 1999 revision, so name one standard in your purchase order.

Use it with

## Tools that work well together.

[Quality**Inspection checklist** A quality inspection checklist lists every check an inspector makes on a lot: quantity and packing, labels and market marks, workmanship, function, measurements, on-site tests and documents.](https://sourcesquid.co/tools/inspection-checklist/)[Suppliers**Supplier health check** A supplier health check is a structured screen of a new factory's identity, capability and working style before you order samples or tooling.](https://sourcesquid.co/tools/supplier-health-check/)[Quality**Drop test planner** A drop test checks that a packed product survives the knocks of handling, and ISTA 1A sets the drop height by packed weight: 76 cm for packs under 9.5 kg, down to 31 cm for 27.7 to 45.4 kg.](https://sourcesquid.co/tools/drop-test-planner/)[Quality**Cpk calculator** Cpk, the process capability index, shows how comfortably a process fits inside its tolerance: it is the distance from the mean to the nearest specification limit divided by three standard deviations.](https://sourcesquid.co/tools/cpk-calculator/)

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