Cleanroom class calculator (ISO 14644-1)
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KEY POINTS
The ISO 14644-1 limit is Cn = 10^N × (0.1/D)^2.08 particles/m³; ISO 5 allows up to 3,520 particles of 0.5 µm or larger per cubic meter. Class 100 in the former US standard (100 particles of 0.5 µm or larger per cubic foot) is equivalent to ISO 5, and Class 1000 to ISO 6. Leading-edge fabs keep wafers at ISO 1 to 2 inside FOUPs and EFEMs.
Inputs
ISO 14644-1 classification covers particle sizes from 0.1 to 5 µm. The number of sampling locations follows Table A.1 of the 2015 edition, which differs from the square-root-of-area rule of the 1999 edition.
Maximum concentration by ISO class (particles/m³, cumulative at and above each size)
| Class | 0.1 µm | 0.2 µm | 0.3 µm | 0.5 µm | 1 µm | 5 µm | FED-STD-209E |
|---|---|---|---|---|---|---|---|
| ISO 1 | 10 | 2 | 1 | — | — | — | — |
| ISO 2 | 100 | 24 | 10 | 4 | — | — | — |
| ISO 3 | 1,000 | 237 | 102 | 35 | 8 | — | Class 1 |
| ISO 4 | 10,000 | 2,365 | 1,018 | 352 | 83 | 3 | Class 10 |
| ISO 5 | 1.00×10⁵ | 23,651 | 10,176 | 3,517 | 832 | 29 | Class 100 |
| ISO 6 | 1.00×10⁶ | 2.37×10⁵ | 1.02×10⁵ | 35,168 | 8,318 | 293 | Class 1,000 |
| ISO 7 | 1.00×10⁷ | 2.37×10⁶ | 1.02×10⁶ | 3.52×10⁵ | 83,176 | 2,925 | Class 10,000 |
| ISO 8 | 1.00×10⁸ | 2.37×10⁷ | 1.02×10⁷ | 3.52×10⁶ | 8.32×10⁵ | 29,251 | Class 100,000 |
| ISO 9 | 1.00×10⁹ | 2.37×10⁸ | 1.02×10⁸ | 3.52×10⁷ | 8.32×10⁶ | 2.93×10⁵ | — |
Cleanliness in semiconductor fabs
An ISO class number means "up to 10 to the power N particles of 0.1 µm or larger per cubic meter," so each step up allows 10 times more particles. "Class 100" in the former US standard means no more than 100 particles of 0.5 µm or larger per cubic foot, equivalent to ISO 5. Names such as Class 100 and Class 1000 are still widely used on the shop floor, including in Japan.
In leading-edge fabs, wafers are kept in environments equivalent to ISO 1 to 2 inside FOUPs and mini-environments (EFEMs), while the bays where people work are designed to around ISO 4 to 6. Carrying wafers in sealed containers costs far less to build and run than making the whole fab ultra-clean.
FAQ
What ISO class is Class 100?
Class 100 in FED-STD-209E is equivalent to ISO 5, Class 1,000 to ISO 6 and Class 10,000 to ISO 7.
How many sampling locations are needed?
The 2015 edition of ISO 14644-1 sets the minimum from the cleanroom area using Table A.1, for example 16 locations for 100 m². This replaced the square-root-of-area rule of the 1999 edition.
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Last updated: October 23, 2026