AQL sampling calculator

How to use it

1. Lot size: the quantity presented for inspection, usually the order quantity of one item or one PO.
2. Inspection level: General level II is the usual choice. Level I gives a smaller sample and level III a larger one. The special levels S-1 to S-4 give small samples, for checks that destroy the product or take a long time, such as carton drop tests or function tests.
3. AQL for each defect class: for consumer goods a common setting is critical 0 (not allowed), major 2.5 and minor 4.0. Your client's specification decides.
4. Draw the sample at random from the whole lot, inspect it and count the defects in each class. The lot passes when every class is at or below its Ac number.

Why the sample size sometimes changes with the AQL

The lot size and the inspection level give a code letter, and each code letter has a sample size. For some combinations of code letter and AQL the table in the standard shows an arrow instead of numbers. The arrow means: use the nearest plan above or below, together with that plan's sample size. This calculator follows the arrows and tells you when it does. If the plan's sample is as large as the lot, inspect every piece.

What AQL does and does not mean

AQL stands for acceptance quality limit. AQL 2.5 does not mean that 2.5% defective pieces are acceptable in every lot. It is the quality level that a sampling plan will accept most of the time: lots at that level usually pass, and worse lots are rejected more and more often. A lot that passes can still contain defects.

What this calculator covers

Single sampling plans for normal inspection (Table I and Table II-A of ISO 2859-1 and ANSI/ASQ Z1.4, which share the same figures), for AQL 0.065 to 6.5. Tightened and reduced inspection and double sampling are not included. Always check the result against your client's requirements.