Lot size in — sample size and Accept/Reject numbers out. Single sampling, normal inspection, the exact table used by our AQL Pocket Inspector app. No signup, nothing uploaded.
The app does this offline, logs individual defects against the plan, and exports a signed PDF inspection report — this page is the free calculator only.
Code letter is Z1.4's shorthand for your lot size + inspection level combination. Sample size (n) is how many units to randomly inspect from the lot. Accept/Reject (Ac/Re) is the maximum number of defective units you can find and still accept the lot (Ac), and the number at which you must reject it (Re) — e.g. "2 / 3" means 0–2 defects passes, 3+ fails.
What is AQL?
Acceptable Quality Limit — the standard statistical sampling method QC inspectors and sourcing agents use to judge a whole production lot by inspecting a random sample, instead of every unit. ANSI/ASQ Z1.4 (equivalent to ISO 2859-1, and the civilian successor to MIL-STD-105E) is the most widely used version worldwide, especially in China sourcing/QC.
Which inspection level should I use?
General Level II is the default for most inspections and is what buyers request unless told otherwise. Level I uses a smaller sample (less discrimination, lower cost); Level III uses a larger sample (tighter discrimination). The S-1 to S-4 "special" levels are for destructive or expensive testing where small samples are required.
Is this calculator accurate?
The lot-size→code-letter and code-letter→sample-size tables (all 7 inspection levels) are shipped with high confidence, cross-checked against the official standard text and multiple independent sources. A handful of Ac/Re cells at the extreme ends of the table (very small lots at tight AQLs, or very large lots at loose AQLs) require Z1.4's "arrow substitution" rule — using a neighbouring code letter's plan — and are flagged below rather than guessed at.
Does this replace a full inspection report?
No — this page only computes the plan. If you need to log which specific units failed and why, attach photos, and generate a shareable PDF report to send a supplier or buyer, that's what the AQL Pocket Inspector app does, fully offline.