IS 2500 provides acceptance sampling plans indexed by AQL (Acceptable Quality Level). It tells you how many samples to inspect and how many defects are acceptable to accept or reject a lot. Adopted from ISO 2859-1. Used across all manufacturing and construction quality control.
Sampling procedures for inspection by attributes, providing single, double, and multiple sampling plans indexed by acceptable quality level (AQL).
Key Values
Inspection levelsI, II (normal), III, S-1 to S-4 (special)
AQL range0.010 to 1000 defects per hundred units
Practical Notes
! IS 2500 answers 'how many to test and when to accept/reject'. IS 4905 answers 'how to select the samples'.
! General Inspection Level II is the default unless otherwise specified.
! Always start with normal inspection. Switch to tightened if 2 out of 5 lots are rejected. Switch to reduced if quality is consistently good.
! AQL is NOT the acceptable defect percentage in a lot — it is the quality level that has a 95% probability of acceptance.