ISO14644-1 is an international standard which is adopted by the US, Europe, Japan, Russia and China at present. The Federal Standard 209A, B, C, D and Eas previously used by the US is no longer used in the country. The Class 100, Class 10000 and Class 100000 as previously known by us are originated from the Federal Standard FS 209B of the US, which have been replaced by the Class 5, Class 6, Class 7 and Class 8 of the international ISO-14644 standard.

The grade standard of the cleanliness of ISO-14644 is shown as follows. 

Cleanroom and suspended particulates in clean air of the cleanliness of ISO-14644

State：① Each time collect at least 3 times
② This standard does not apply to characterize the Suspended particulates physical, chemical, radiological and living.
③According to the technological requirements, the size of particles can be determined 1-2 particle diameter
④ According to the requirements of the particle size D allowable maximum concentration determined by the next type (particle diameter of 0.1 mu m mu m~5)
（pcs/m3）
Where, N refers to the value of cleanliness Class 1~9, between them 0.1 can be interpolated as minimum unit incremental change.