Cleanroom Classifications – Classes 1, 10, 100, 1000, 10000, & 100000

08 Jan.,2024


The FS209E cleanroom classification system has six cleanroom cleanliness classes: Class 1, Class 10, Class 100, Class 1,000, Class 10,000, and Class 100,000. ISO 14644-1 replaced FS209E in 1999 for Europe and in 2001 for the United States. The ISO classification adds two cleaner standards and one dirtier standard for a total of nine classifications. To learn more about ISO standards, read our article Cleanroom Classifications (ISO 8, ISO 7, ISO 6, ISO 5).

The cleanroom given names under Federal Standard 209e are:

  • Class 100,000 clean room (dirtiest)
  • Class 10,000 clean room
  • Class 1,000 clean room
  • Class 100 clean room
  • Class 10 clean room
  • Class 1 clean room (cleanest)

Despite the obsolescence of the FS209E classifications, the terms and names used for cleanrooms continue to be used in popular language as references, especially in specific industries such as the semiconductor sector.

This article aims to demystify the nuances between the FS209E and the ISO 14644-1 standard and to help you better understand the details and requirements of the former cleanroom classification system.

To learn more about cleanroom classifications, read our featured articles:

Cleanroom Classifications and Particles Count

By definition, cleanrooms are classified based on how clean the air is. The maximum number of particles allowed varies depending on the cleanroom classifications you wish to obtain.

Inside 209E cleanrooms, the particles equal to and greater than 0.5µm are measured in 1 cubic foot of air, whereas ISO classes are in cubic meters of air.

Below is the graphic chart showing the maximum particle count for the Federal Standard 209E and its ISO standards equivalent.

Federal Standard 209E Class Limits


Particles / ft³

ISO Equivalence






Class 1 35 7.5 3 1 N/A ISO 3 Class 10 350 75 30 10 N/A ISO 4 Class 100 N/A 750 300 100 N/A ISO 5 Class 1,000 N/A N/A N/A 1,000 7 ISO 6 Class 10,000 N/A N/A N/A 10,000 70 ISO 7 Class 100,000 N/A N/A N/A 100,000 700 ISO 8

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