AQL sample size calculator

What AQL means

AQL stands for Acceptance Quality Limit. It's the worst defect rate you're prepared to accept on average, written as a percentage. An AQL of 2.5 for major defects means you accept that around 2.5 in every 100 units may have a major defect.

Instead of checking every unit, an inspector checks a random sample. The sampling tables in ISO 2859-1 (the same tables as ANSI/ASQ Z1.4) tell you how big that sample should be and how many defects it can contain before the whole order fails.

How to read your result

Sample size is how many units the inspector pulls at random from the finished, packed goods. Accept is the most defects of that type the sample can contain and still pass. Reject is the number at which the order fails.

Each defect type is judged on its own. If the sample passes on major defects but fails on minor ones, the order fails.

Sometimes a low AQL needs a different sample size from the one the code letter suggests. The standard handles this with arrows in its table, and the calculator follows them for you, so critical, major and minor defects can show different sample sizes.

Which levels importers usually choose

General inspection level II is the default for most consumer goods. Level I uses a smaller sample (cheaper, less certain); level III a bigger one. The special levels S-1 to S-4 are for tests that are slow or destroy the product, such as drop tests.

A common set-up is 0 critical defects allowed (anything unsafe or illegal), 2.5 for major defects (the product doesn't work as it should or wouldn't sell) and 4.0 for minor defects (small cosmetic issues). Agree yours with the supplier in writing before production starts.