ISO 14644 Cleanroom Classification Standards

The particle limits behind ISO 5, ISO 7, and ISO 8, the occupancy states that give them meaning, and how ISO classes map to USP, FDA, and EU requirements.

ISO 14644 is the international standard series for cleanrooms and associated controlled environments. Part 1 defines cleanroom classification by airborne particle concentration, and it is the reference behind almost every cleanliness requirement you will encounter: the ISO 5 in a compounding cabinet, the ISO 7 in a pharmacy buffer room, the Grade B in a European sterile fill line.

This page gives the classification table, explains the three occupancy states that make a class meaningful, and shows how ISO classes line up with the regulations our customers work under.

The ISO 14644-1 classification table

ISO 14644-1:2015 defines nine classes by the maximum concentration of airborne particles per cubic meter, at each of six particle sizes. Lower numbers are cleaner. Each limit is cumulative, meaning it counts all particles of that size and larger.

Maximum permitted particle concentrations in particles per cubic meter of air, from ISO 14644-1:2015. Values restated in our own layout with attribution to ISO. Cells marked n/a are those where the standard sets no limit, because classification at that particle size is not applicable to that class.

Those n/a cells are not omissions, and they are the detail most reproductions of this table get wrong. ISO 14644-1 leaves them deliberately empty for two different reasons.

• At the clean end, the concentrations are too low to measure reliably. Sampling a large enough air volume to count them with statistical confidence is impractical, so classification at those sizes is inappropriate.
• At the dirty end, the concentrations of small particles are so high that the particle counter cannot resolve them. ISO 7, ISO 8, and ISO 9 are therefore classified only at 0.5 µm and above.

The 2015 second edition removed four cells that appeared in the 1999 first edition: ISO 1 at 0.2 µm, ISO 2 at 0.5 µm, ISO 3 at 1 µm, and ISO 5 at 5 µm. The last of those is the one people notice, because ISO 5 at 5 µm was widely used in pharmaceutical monitoring. If a chart still shows a value of 29 in that cell, it is reproducing the 1999 table.

This is worth checking on any reference chart you use, including ours. A table that fills every cell with a number is showing you either the withdrawn 1999 edition or an interpolation that the standard does not sanction.

A class without a state is not a specification

The single most common mistake in a cleanroom specification is naming a class and stopping there. “ISO 7” on its own does not describe a room. ISO 14644-1 defines three occupancy states, and a room can pass in one and fail in another.

The gap between at-rest and operational is where cleanrooms disappoint. People are the largest particle source in any cleanroom, and a room that holds ISO 7 empty can sit well outside it with four gowned staff working. Specify the state you need, and test in it.

• USP <797> requires certification under dynamic operating conditions, which is the operational state. See our USP <797> page.

How classification is verified

The 2015 edition changed how a room is proven to meet its class, and the changes are still not universally applied.

• Sampling locations come from a lookup table. The 1999 edition used a square-root formula based on room area. The 2015 edition replaced it with a table that generally requires more locations, particularly in larger rooms.
• The statistical basis changed. Classification now demonstrates, with 95% confidence, that at least 90% of the room complies with the class limit. It is a statement about the room as a whole, not about the individual points sampled.
• The 95% upper confidence limit calculation was removed. The 1999 edition required it where between two and nine locations were sampled. The 2015 edition does not.

Practically, this means a room certified under the 1999 method may have been sampled at too few locations to satisfy the current standard. It is worth confirming which edition your certifier is working to.

The parts of the series

ISO 14644 is a series, not a single document, and each part is revised on its own cycle. These are the parts that most often apply to a project.

Part 1 is the second edition, published in December 2015. It was reconfirmed in 2021 and entered systematic review in July 2026, so it remains the current edition.

The parts move independently, and three of them changed recently. Parts 13 and 14 received second editions on February 25, 2026, and Part 15 followed on May 12, 2026. Part 13 was also retitled: it now covers cleaning of surfaces in terms of particle and chemical concentration, where the withdrawn 2017 edition did not name chemical concentration. If you are working from a 2016 or 2017 copy of any of those three, you are working from a withdrawn document.

How ISO classes map to other standards

Most of our customers are not working to ISO 14644 alone. They are working to a regulation that references it. This is how the classes line up.

FED-STD-209E was cancelled in November 2001 and is shown for reference only, because the Class 100 and Class 10,000 shorthand is still in everyday use. Grade equivalences are approximate: EU GMP Annex 1 sets its own limits and occupancy states, and they do not map one to one.