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ISO 14644-1 Cleanroom Class Reference (Particle Limits and FS 209E)

ISO 14644-1 sets the cleanroom class from the number of airborne particles per cubic meter at stated sizes. Specifications, vendor quotes and audit documents still mix ISO classes and the old Federal Standard 209E names, so this table puts both side by side with limits for each particle size and typical uses in photonics and optics.

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ISO class	FS 209E equivalent	0.1 um and larger	0.2 um and larger	0.3 um and larger	0.5 um and larger	1 um and larger	5 um and larger	Typical photonics use
ISO 1	none	10	2	-	-	-	-	Semiconductor lithography research, not typical for photonics assembly
ISO 2	none	100	24	10	4	-	-	Specialized semiconductor and nanotechnology work
ISO 3	Class 1	1,000	237	102	35	8	-	Advanced photomask and wafer work
ISO 4	Class 10	10,000	2,370	1,020	352	83	-	High-end optics coating chambers and wafer fabrication
ISO 5	Class 100	100,000	23,700	10,200	3,520	832	see note	Laser optics final assembly, coating load and unload, fiber end-face work in laminar flow hoods
ISO 6	Class 1,000	1,000,000	237,000	102,000	35,200	8,320	see note	Precision optics assembly and sensitive laser module build
ISO 7	Class 10,000	-	-	-	352,000	83,200	2,930	General optical subassembly, fiber optic component assembly, lens cementing
ISO 8	Class 100,000	-	-	-	3,520,000	832,000	29,300	Gowning areas, packaging, kitting and non-critical inspection
ISO 9	none	-	-	-	35,200,000	8,320,000	293,000	Ordinary room air, controlled background areas

Limits are maximum allowed particles per cubic meter at the stated size and larger, for the at-rest, as-built or operational state you specify, using the ISO 14644-1 formula Cn = 10^N x (0.1/D)^2.08. The 5 um column for ISO 5 and 6 depends on the edition of the standard and the sampling rules, so check your copy. Dashes mean the size is not applicable for that class. FS 209E was withdrawn in 2001 but its class names remain common in specifications.

Cleanroom records tied to lots

Optional: an expert look at linking particle counts, certification dates and gowning logs to production lots in your ERP.

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How to use the table

Search for a class such as ISO 5 or for the legacy name such as Class 100 to find the matching row. Read across to see the maximum number of particles per cubic meter at each size. Use the last column to sanity check whether a class suits your process. Optics coating and laser final assembly usually need ISO 5 at the point of work, which is often achieved with a laminar flow hood inside an ISO 7 room. The page exports to PDF or Excel for inclusion in a cleanroom specification or a supplier requirement.

State the occupancy: as-built, at-rest or operational
State the particle size you test at
Specify the room class and the point-of-work class separately
Match your particle counter calibration to ISO 21501-4

The formula behind the table

ISO 14644-1 defines the class limit for a particle size D in micrometers as Cn equals 10 to the power N times (0.1 divided by D) to the power 2.08, where N is the ISO class number. For ISO 5 and 0.5 um that gives about 3,520 particles per cubic meter. The same formula yields every cell in the table. It also shows why one particle size dominates: moving one class up or down changes every limit by a factor of ten.

Choosing a class for optics work

A particle on an optic can scatter light, absorb laser energy and start a damage site. High-power laser optics, low-loss coatings and fiber end faces therefore need clean handling. A practical pattern is an ISO 7 or ISO 8 background room, ISO 5 laminar flow stations where optics are open, and strict gowning and cleaning procedures. Over-specifying the whole room to ISO 5 drives air handling cost sharply upward, so focus the clean zone on the open work.

Common mistakes

Quoting only the class without the state of occupancy is the most common gap, since at-rest and operational counts differ widely. Another is reading the 0.5 um limit as if it covered all sizes. Teams also confuse FS 209E cubic feet limits with cubic meter limits: Class 100 means 100 particles per cubic foot at 0.5 um, roughly 3,520 per cubic meter. And cleanroom class is not the same as cleanliness of a part: surface cleanliness needs its own specification.

Frequently Asked Questions

What is ISO 5 equal to in Federal Standard 209E?

ISO 5 corresponds to Class 100, meaning 100 particles per cubic foot at 0.5 um and larger. In metric terms that is about 3,520 particles per cubic meter. FS 209E was withdrawn in 2001, but the names are still used.

Is ISO 7 enough for fiber optic assembly?

Many fiber optic component builds run in an ISO 7 or ISO 8 room, with inspection and connector end-face work done in a laminar flow hood. The right level depends on your loss and reliability targets and your customer specification.

How often must a cleanroom be reclassified?

ISO 14644-2 sets monitoring plans. For ISO 5 and cleaner, the standard calls for classification testing at least every 6 months, and for ISO 6 and dirtier at least every 12 months, with continuous or periodic monitoring as your risk assessment requires.

Does the class include the 0.1 um column for ISO 7?

No. For ISO 7 and higher classes the smaller sizes are not applicable in the table, which is why they show dashes. Classification for those classes is based on 0.5 um and larger sizes.

If cleanroom particle counts, gowning logs and certification dates are tracked in your ERP or quality system, Netray can help build read-only dashboards and alerts on your own infrastructure.

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