AQL Sampling Calculator: Sample Size, Ac and Re

AQL, or acceptance quality limit, is a quality index agreed in advance to select a sampling plan. It does not guarantee that a shipment contains no more than a stated percentage of nonconforming products. To use it, define the inspection lot, agree the defect class and AQL, select the inspection level, then obtain the sample size and acceptance/rejection numbers from the relevant tables.

The calculator below uses normal inspection and single sampling, with general inspection levels I, II or III. It counts nonconforming units within one agreed defect class. It does not count every individual defect as a separate unit or determine whether a product is safe.

Go to the AQL calculator.

What the AQL number tells you

Values such as 0.65, 1.0, 1.5, 2.5 and 4.0 identify columns in the sampling table. Choose the value with the responsible buyer and supplier before inspection, alongside clear defect definitions and the standard edition used in the contract. Do not multiply the lot size by the AQL to obtain an acceptance allowance.

AQL 2.5 is commonly used for major defects in general consumer-product inspection, as described by Eurofins. It is not a default for every product, function or hazard. Material, intended use, customer requirements and consequences of failure can justify a different requirement. Treat the calculator’s initial 2.5 selection as an example to replace with the agreed value.

This page explains the lookup and the count-based decision. For deciding whether an acceptance-sampling approach suits the purchase in the first place, use the separate guide to fitting a sampling plan to buying risk.

Read the plan: lot size, sample size, Ac and Re

• Lot size is the number of units in the defined batch being assessed. Record which models, variants, production batches and cartons belong to it. Do not silently combine unrelated goods to obtain a more convenient plan.
• Sample size is the number of units to inspect under the selected plan. Select units randomly across the lot; a supplier-selected set of good-looking units is not a random sample.
• Ac is the acceptance number: the largest number of nonconforming units that permits acceptance on that criterion.
• Re is the rejection number: the number at which the lot is rejected on that criterion.

Count a unit once within the defect class being assessed, even if that unit has several defects in that class. Define how units are classified across classes in the inspection instructions. The calculator is not a method for pooling major, minor and critical findings into one total.

Example: a lot of 20,000 units

For 20,000 units, level II and AQL 2.5, Table I gives code M. The normal single-sampling master table gives 315 units, Ac 14 and Re 15. With 14 nonconforming units in the agreed class, this criterion permits acceptance. With 15, it requires rejection. The decision still depends on the agreed critical-defect and other inspection requirements.

This does not mean that 14 divided by 315 estimates a guaranteed defect rate for the entire shipment. It is a rule for deciding what to do with that lot on the basis of the prescribed sample.

A small-lot example and the arrow rule

For 27 units, level II and AQL 2.5, Table I gives code D. In Table II-A, the arrow points upward to plan C: inspect 5 units, Ac 0, Re 1. Zero nonconforming units permits acceptance on that criterion; one or more requires rejection. ASQ’s published explanation walks through this exact example.

An arrow changes the plan’s sample size as well as its Ac/Re values. Do not keep D’s nominal sample size while using C’s limits. The calculator displays the initial code and explains the destination plan when an arrow applies. If the required sample equals or exceeds the lot size, the table note calls for 100% inspection; the result shows the entire lot as the number to inspect.

Inspection levels and switching rules

General inspection level II is the starting selection in this calculator. Level I generally gives a smaller sample-size code and level III a larger one for the same lot size; the master table’s arrows can affect the final sample. Agree the level before drawing units.

Level I does not mean reduced inspection, and level III does not mean tightened inspection. Inspection level and inspection severity are separate choices. This calculator always uses the normal-inspection master table.

ASQ describes Z1.4 as a system for a continuing stream of lots with switching rules. An adverse acceptance history can trigger tightened inspection; an eligible record of accepted lots and stable production can support reduced inspection under the standard’s conditions and the responsible authority’s decision. Failed reduced-inspection conditions bring inspection back to normal. Keep the lot history and apply the edition’s complete rules; changing the level selector here does not implement those transitions.

Three mistakes that change the meaning of the result

“The sample passed, so every unit is good.” Sampling leaves uncertainty about uninspected units. Keep the result tied to the sampled lot, defect class and method. Record the actual findings and separately assess safety, function and any requirements outside this sampling criterion.

“We can change the AQL after seeing the findings.” A different AQL can produce a different acceptance limit, but it does not alter the observations already recorded. Do not overwrite the original plan or relabel its result as a pass. Document any authorized disposition or reinspection separately under the applicable rules.

“An AQL result covers critical defects.” Agree critical-defect criteria separately. Safety defects, or functional failures classified as critical for the intended use, may need a separate rejection rule, testing or a different inspection method. There is no AQL 0 column in this calculator; zero-acceptance requirements need their own explicit agreement.

How does a certificate of conformity fit with AQL inspection?

A certificate of conformity or conformance (CoC) is a statement that identified goods meet stated requirements. Its meaning depends on the issuer, scheme, scope and supporting evidence. A supplier’s order declaration, a regulated certificate and an independent inspection report are not interchangeable documents.

For example, CPSC’s General Certificate of Conformity (GCC) guidance concerns certain regulated general-use consumer products in the United States. It identifies the responsible manufacturer/importer, applicable rules and supporting testing information. Children’s-product certification follows different requirements. Do not assume a supplier PDF titled “CoC” satisfies either route; ask the responsible product-compliance specialist which requirements and current filing process apply.

Compare what each record actually establishes

Record	Question it can help answer	What remains separate
Supplier conformity statement	What requirements does this issuer claim the identified goods meet?	Authenticity, evidence basis, applicable market rules and shipment linkage
AQL inspection report	What was found in the selected units under the agreed plan?	Uninspected units, untested characteristics and any separate compliance requirements
Laboratory report	What did the identified specimens achieve under the stated method?	Whether specimens represent this lot and whether every applicable requirement is covered

Passing the sampling criterion does not authenticate a certificate or turn it into a compliance decision. A certificate does not erase an inspection failure. Keep both records, including their original observations, and have the authorized buyer or specialist resolve a conflict before release. QIMA’s inspection conditions likewise distinguish the requested service and report from an infallible assessment.

Reconcile identity before relying on either document

1. Match the legal issuer, product/model and specification revision.
2. Connect production dates, lot/carton IDs and quantities to the actual shipment.
3. Record the claimed requirements, report references and issuing body’s verification route.
4. Compare the inspection scope with the characteristics covered by the declaration or testing.
5. Record missing evidence and its owner; do not replace a missing report with a changed AQL.

Use the product specification sheet to define the requirements and the shipping-mark checklist to keep carton identity consistent. The calculator below remains the same normal single-sampling lookup; it does not issue a certificate or establish that every unit is conforming.

Calculate your sampling plan

Enter the lot size, select the agreed AQL and choose the general inspection level. Calculate once for each defect class with its own AQL. Accept/reject counts refer to nonconforming units in that class, not the combined number of defects found.

Table sources and scope

The lookup is based on ANSI/ASQ Z1.4-2003, Table I and Table II-A, using the published tables available from Pro QC: Table I — sample-size code letters and Table II-A — normal single-sampling master table. The five AQL columns supported here are 0.65, 1.0, 1.5, 2.5 and 4.0. Arrows are followed within the selected column; values are not interpolated or calculated from a percentage formula.

Use the standard edition named in your contract. ISO lists ISO 2859-1:2026 as its current edition; this calculator’s identified table basis remains ANSI/ASQ Z1.4-2003. It does not claim validation against the 2026 ISO edition, provide tightened or reduced tables, or choose a switching status. Unsupported or unverified combinations are Not established.

For the inspection report, retain the lot definition, AQL, defect class, level, normal/single status, initial code, actual sample size, Ac/Re, unit-selection method and findings. After calculating the sample, use the China pre-shipment inspection checklist to organize what to check before shipment release.

Sources

• ASQ — Z1.4 and Z1.9 standards, scope and switching system
• Pro QC — published ANSI Z1.4-2003 sampling tables
• ASQ — worked 27-unit, level II, AQL 2.5 example
• Eurofins — AQL use in consumer-product inspection
• ISO — ISO 2859-1:2026 edition and standard history