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AQL calculator ISO 2859-1

Enter lot size and AQL — instantly see code letter, sample size, Accept and Reject numbers per ISO 2859-1 (Normal Inspection, General Level II, single sampling). No Excel table, no waiting.

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Number of pieces in the lot you are receiving (e.g. 1,000). Whole number ≥ 2.

Maximum acceptable percentage of non-conforming pieces. Common in automotive: 0.65 or 1.0.

MVP scope: Normal Inspection · General Level II · single sampling plan · AQL 0.65–6.5. For Tightened / Reduced, Levels I/III/S-1..S-4, double/multiple sampling plans, or switching rules use the official ISO 2859-1 PDF — or ask the QualityOS AI assistant.

How an AQL Sampling Plan works

Short reference for anyone who needs to know where the numbers come from.

Procedure (single sampling plan)

  1. From the lot size, look up the code letter (Table 1, General Level II).
  2. From the code letter and AQL, look up sample size (n) + Ac (Accept) / Re (Reject) (Table II-A, Normal Inspection).
  3. Take n pieces at random from the lot. Count the non-conforming pieces.
  4. If non-conforming ≤ Ac → accept the lot. If ≥ Re → reject.

What AQL values mean

AQL (Acceptable Quality Limit) is the maximum percentage of non-conforming pieces you still consider acceptable as a long-term average. At AQL = 1.0 %, a supplier holding 1 % defectives has a high probability that lots pass; at 2 %, acceptance drops sharply. For automotive incoming inspection the typical settings are AQL 0.65 % (critical) to 1.0 % (standard). Cosmetic non-functional can move to 2.5–4.0 %.

Levels, severity, sampling type

ISO 2859-1 has 3 General Levels (I = small samples, II = default, III = large samples) plus 4 Special Levels (S-1 to S-4). Severity has 3 modes: Normal (default), Tightened (after a string of rejections), Reduced (after a string of acceptances). Sampling type can be Single / Double / Multiple. This calculator covers the most common case: General Level II + Normal + Single. For other scenarios use the official ISO 2859-1 or ask the QualityOS AI assistant.

Frequently asked questions

Which AQL should I use for automotive incoming inspection?
For automotive Tier 1 / Tier 2 suppliers, the typical AQL is 1.0 % for standard functional characteristics and 0.65 % for critical / safety characteristics. For cosmetic non-functional (surface scratches, minor aesthetic defects) you can go to 2.5 or 4.0 %. Verify the current values in your customer CSR (VW Formel Q, Stellantis SQAM, Ford Q1) or your Quality Agreement.
What do the arrows in ISO 2859-1 table mean?
The arrow ↑ (up) means "use the plan from the row above" and ↓ (down) "use the plan from the row below". You meet them in the top-left and bottom-right corners of Table II-A. The reason: at small lot sizes + tight AQL the lot itself would have a small sample size — ISO forces you to take a larger sample (from a plan below) so that Ac/Re has statistical power. This calculator follows the arrows automatically and the result tells you "original code letter X, used Y".
What is the difference between General Level II and III?
Level II is the default and accounts for ~95 % of use cases. Level III gives larger samples for higher discrimination — suitable for characteristics where the customer requires stronger confidence in the decision. Level I gives smaller samples — for cost-sensitive or destructive tests. Special Levels (S-1 to S-4) are for very small sample sizes, typically destructive or expensive tests. This MVP calculator covers Level II.
Single, Double or Multiple Sampling Plan — which to pick?
Single Sampling (what this calculator does) is simplest — take n pieces, decide once. Double Sampling gives you a second chance: if the first sample lands in an "indecisive" zone, take another and decide based on both. Multiple goes up to 7 samples. Double + Multiple are more efficient (on average fewer pieces tested) but more complex. For most incoming inspection scenarios, Single is sufficient.
How do I switch back from Tightened to Normal inspection?
Switching rules per ISO 2859-1: Normal → Tightened when 2 of 5 consecutive lots are rejected. Tightened → Normal when 5 consecutive lots are accepted (under Tightened). Tightened → STOP inspection if 5 lots are rejected under Tightened. Normal → Reduced when 10 consecutive lots accepted + qualifying conditions. This calculator does not implement switching rules — it always computes Normal.

Built by an automotive quality engineer

Your incoming inspection team has this table open every day.

12 years in automotive quality. Production Quality Leader at HELLA-Forvia Kočovce — 24-person QA team across 2 factories, including Receiving Inspection. I know the AQL table by heart for AQL 1.0 + lot size 50–500, but for the rest I always had to reach for the PDF. This is the faster version.

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The plan says Reject. The AI helps you with the supplier complaint.

When an AQL plan flags a lot as rejected, the QualityOS AI Assistant helps with containment actions, root-cause analysis (5 Why, Ishikawa) and a customer-facing 8D report for your supplier in their language and format.

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