Acceptance Sampling Plan Calculator

Acceptance sampling lets a quality team inspect a small, statistically defensible sample from a lot instead of every unit, then decide to accept or reject the whole lot based on how many defects turn up. This calculator implements a simplified version of the ANSI/ASQ Z1.4 (ISO 2859-1) sampling scheme: Lot Size maps to a sample-size "code letter" through a lookup table matching the standard's own lot-size bands. Inspection Level then adjusts the plan's strictness from the Normal baseline: Reduced (after a sustained run of good lots) pulls a smaller sample, while Tightened (after recent quality problems) keeps the same sample size but demands a stricter Accept Number -- one fewer defect is tolerated than Normal would allow at the same sample size. The Accept Number is derived from the sample size and your Acceptable Quality Level (AQL) -- the maximum defect rate still considered acceptable -- as the smallest defect count where the plan still accepts a lot sitting exactly at AQL roughly 95% of the time, and the Reject Number is one more defect than that.

Because the lookup table groups a wide range of lot sizes into the same code letter, moving Lot Size by a small amount often doesn't change Sample Size at all -- only a Lot Size that crosses one of the table's own band boundaries changes which code letter, and therefore which sample size, applies. The operating-characteristic figures (P(Accept) at AQL, Average Outgoing Quality, estimated LTPD, and Average Total Inspection) describe how the plan performs statistically, not just what sample size to pull. This is a planning aid for understanding sampling-plan mechanics, not a substitute for a full ANSI/ASQ Z1.4 table lookup in a regulated quality system.