There are two commonly used cleanroom cleanliness levels.
One is the U.S. federal 209E, which has been abolished, but in China has been accustomed to, or often used, what we call the 100, 10,000, 100,000, etc. is in accordance with this level.
It refers to the concentration of 0.5μm dust particles in 1 cubic foot (ft?), such as 100 is 100, 1000 is 1000, 10000 is 10000, so the smaller the value, the higher the level.
The other is the international standard ISO14644, also the smaller the value, the higher the cleanliness level. It refers to the number of dust particles in 1 cubic meter (m?) of various specifications. This grade and the U.S. federal 209E standard can be corresponding.
Such as the U.S. Federal 209E hundred level corresponds to ISO14644 level 5, 1m? 0.5μm dust particles in 3520; 1000 level corresponds to ISO14644 level 6, 1m? 0.5μm dust particles in 35200 ...... and so on, and so on.
Cleanroom class standard division