AQL sampling calculator

ANSI/ASQ Z1.4-2003 (R2018), equivalent to ISO 2859-1. Step 1: the lot size and inspection level (General Level II is the default) give a sample-size code letter, whose letter fixes the sample size n (e.g. code L = 200 pieces). Step 2: the code letter and AQL give the Accept (Ac) and Reject (Re) numbers from the single-sampling normal plan (Re = Ac + 1).

Inspect n random pieces; accept the lot if defects ≤ Ac, reject if ≥ Re. AQL is the maximum percent defective that is routinely accepted over a stream of lots — a producer-risk quality level, not a target or a guarantee for the single lot in front of you.

A 4,000-piece lot at General Level II → code L → inspect 200; at AQL 2.5 accept with ≤10 defects, reject at ≥11; at AQL 4.0 accept ≤14, reject ≥15. A common hardware clause uses AQL 0 critical / 2.5 major / 4.0 minor.

Where the standard shows an arrow, small lots switch to a larger or smaller sample size, and when the sample would reach the lot size you inspect 100%. This is an attributes plan (defect counts, not measurements), and the full standard adds tightened/reduced switching rules; a single normal plan is a simplification. The published Ac/Re follow Z1.4 — including the Ac = 0 acceptance diagonal, so a plan calling for zero defects rejects a lot with even one.