The lower the particle concentration, the higher the classification of the cleanroom. ISO 14644-1 provides an international standard for classifying cleanrooms. The International Organization for Standardization – ISO for short – is an independent organization dedicated to setting international standards for procedures.
The ISO clean room classes are identified by the numbers 1-9. ISO 1 is the cleanest possible room, ISO 9 corresponds to almost normal room air. The permitted number of airborne particles per ISO class can be found here.
