Technical reference
Cleanroom classes: ISO 14644 and the US Class numbers
Most US teams still describe a room as Class 100, 1,000 or 10,000. The active standard is ISO 14644-1. This page gives both, with particle limits in particles per cubic metre and per cubic foot, so there is no ambiguity about what is being specified.
Class equivalence and particle limits
Limits shown are for particles equal to or larger than 0.5 µm, the size most commonly used to compare cleanroom classes.
| ISO 14644-1 | FS 209E (US, cancelled 2001) | Particles ≥0.5 µm / m³ | Particles ≥0.5 µm / ft³ | Typically used for |
|---|---|---|---|---|
| ISO 3 | Class 1 | 35 | 1 | Critical semiconductor lithography and mask areas |
| ISO 4 | Class 10 | 352 | 10 | Advanced semiconductor fab critical process areas |
| ISO 5 | Class 100 | 3,520 | 100 | Semiconductor fab and critical process zones |
| ISO 6 | Class 1,000 | 35,200 | 1,000 | Semiconductor packaging and test, precision optical assembly |
| ISO 7 | Class 10,000 | 352,000 | 10,000 | Electronics assembly, advanced packaging (flip chip / fan-out / WLP) |
| ISO 8 | Class 100,000 | 3,520,000 | 100,000 | High-density compute and server assembly, optical module assembly, less critical assembly areas |
| ISO 9 | — | 35,200,000 | 1,000,000 | Controlled environment rather than a cleanroom |
Where the numbers come from
ISO 14644-1 defines the limit as Cn = 10^N × (0.1 / D)^2.08, where N is the class number and D the particle size in µm. You can check the table with it: ISO 5 at 0.5 µm gives 3,517 particles per m³, which is the value in the table above.
A note on FS 209E
US Federal Standard 209E was cancelled on 29 November 2001 and replaced by ISO 14644-1. The Class numbers are no longer an active standard, but they remain common shorthand in US industry. When a US customer says “Class 10,000”, we confirm it means ISO 7 in writing rather than assuming.
What we supply at each class
ISO 5–6 · Class 100–1,000
Full-coverage unidirectional airflow, ULPA/HEPA ceilings, tight temperature and humidity control, and monitoring designed in from the start rather than added later.
ISO 7 · Class 10,000
The workhorse class for electronics assembly and advanced packaging. FFU-based layouts with local laminar zones where the process actually needs them.
ISO 8 · Class 100,000
The practical choice for high-density compute and server assembly. Continuous particle, temperature and ESD monitoring proves it stays in class.
Supplying a US project
Delivering equipment into the United States is not the same as delivering it domestically. These are the points we handle up front.
Electrical: 480 V / 3-phase / 60 Hz
Equipment supplied for US sites is specified for North American voltage, phase and frequency, with UL-listed components where the project requires it, rather than being adapted from a 50 Hz build after the fact.
Dual units throughout
Submittals and specifications are issued with metric and US customary units side by side — airflow in m/s and ft/min, dimensions in mm and inches, capacity in kg and lb — so no one has to convert on site.
Documentation for US submittal review
Drawing packages, material certificates, filter test reports and FAT records can be prepared in the format your submittal process expects, in English.
Freight, offloading and installation support
Modular systems are designed for container shipping, with crating and labelling for US delivery, and installation supervision or commissioning support can be quoted per project.
Time zone and communication
US projects are handled with a named engineer and scheduled calls that work across time zones. We would rather agree a realistic response window than promise instant replies we cannot hold.
Standards that matter for US projects
Referenced as design and documentation alignment, not as a blanket certification claim. Whether a specific standard applies — and what compliance requires — is confirmed per project with your engineers and the local Authority Having Jurisdiction (AHJ — the city, county or state body that inspects and approves the installation; it varies by location).
ISO 14644-1 / -2
Classification and monitoring of cleanroomsThe classification basis used worldwide, including in the US. Part 2 covers the monitoring that proves the room still meets its class after handover — which is also what our environmental monitoring systems are built around.
IEST-RP-CC series
Recommended practices (US, Institute of Environmental Sciences and Technology)The practices US cleanroom engineers most often specify for HEPA/ULPA filter testing, leak testing and room performance verification. Our verification scope is aligned with these methods.
FS 209E
US Federal Standard 209E (cancelled 29 November 2001)No longer an active standard, but US teams still describe rooms as Class 100 / 1,000 / 10,000 / 100,000. We quote in both systems so there is no ambiguity about what is being supplied.
NFPA 318
Protection of semiconductor fabrication facilitiesGoverns fire protection expectations in US fab-type buildings. It affects material selection (fire rating of sandwich panels), detection and egress — relevant when our room sits inside a US facility.
UL listing / NEC (NFPA 70)
Equipment safety listing and electrical installationUS authorities generally expect listed components and NEC-compliant installation. Fan filter units, control panels and monitoring hardware can be specified with UL-listed components for US projects.
ASHRAE 62.1 / 90.1
Ventilation and energyVentilation rates and energy requirements that US mechanical engineers design to. Our air handling scope can be coordinated with the project's ASHRAE basis of design.
Not sure which class your process actually needs?
Send us the process, the equipment list and the area and our engineers will tell you the class that fits — including where a lower class is the right answer.