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Short answer
ISO Class 5 is a cleanroom air-cleanliness class that allows no more than 3,520 particles per cubic metre at 0.5 micrometres and larger. FDA’s aseptic processing guidance treats it as equal to the older “Class 100” label and approximately equal to EU GMP Grade A, and uses it for the critical area where sterile product is exposed.
Definition and scope
ISO 14644-1 assigns cleanrooms a numbered class by the concentration of airborne particles. FDA’s Guidance for Industry: Sterile Drug Products Produced by Aseptic Processing (September 2004) reproduces the designations in its Table 1 and notes that ISO 14644-1 “provide uniform particle concentration values for cleanrooms in multiple industries.” In that table ISO 5 is 3,520 particles per cubic metre at 0.5 µm and larger, which matches the legacy label “Class 100” (100 particles of 0.5 µm per cubic foot).
The same footnote says an ISO 5 particle concentration “is equal to Class 100 and approximately equals EU Grade A.” The word “approximately” matters: the two frameworks are written separately, and the equivalence is a particle-concentration comparison, not a statement that the rules around them are identical. For the full ISO 1 to ISO 9 ladder see cleanroom classifications.
How ISO Class 5 is used in practice
FDA: the critical area
FDA’s guidance names ISO 5 (Class 100) as the condition for the “critical area”, the zone where sterilized drug product, containers and closures are exposed, such as during aseptic connections or sterile ingredient additions before and during filling and closing. Three details in the text are easy to miss:
- Where the count is taken. Air near exposed sterilized containers and closures should hold no more than 3,520 particles of 0.5 µm and larger per cubic metre, counted at representative locations “normally not more than 1 foot away from the work site, within the airflow, and during filling/closing operations.”
- How often. Monitoring should be performed during each production shift, and FDA recommends a remote counting system for non-viable particles, which gives more comprehensive data and is generally less invasive than portable counters. See portable vs remote particle counters.
- Microbiology is a separate expectation. A footnote states that samples from Class 100 (ISO 5) environments “should normally yield no microbiological contaminants.” The ISO 5 number itself covers particles only.
FDA also says the area adjacent to the aseptic processing line should meet at least Class 10,000 (ISO 7) under dynamic conditions, and that ISO 8 is appropriate for less critical activities such as equipment cleaning. A positive pressure differential of at least 10 to 15 pascals is recommended between adjacent rooms of differing classification with doors closed. Isolators are expected to meet Class 100 (ISO 5) in their interior.
EU GMP Annex 1: Grade A
The European Commission’s Annex 1, Manufacture of Sterile Medicinal Products (C(2022) 5938 final, August 2022), defines Grade A as the critical zone for high-risk operations such as the aseptic processing line and filling zone. Its Table 1 sets the Grade A limit at 3,520 particles per cubic metre at 0.5 µm, both at rest and in operation. It also says classification is part of qualification, using total particle concentration measured under simulated operations, with sampling locations per ISO 14644 Part 1. For the wider Annex 1 context see EU GMP Annex 1.
Related classes and a classification versus monitoring gap
The table below uses only FDA’s Table 1 values for particles at 0.5 µm and larger.
| ISO class | Legacy name | Particles per m³ (≥0.5 µm) |
|---|---|---|
| ISO 5 | Class 100 | 3,520 |
| ISO 6 | Class 1000 | 35,200 |
| ISO 7 | Class 10,000 | 352,000 |
| ISO 8 | Class 100,000 | 3,520,000 |
The neighbouring class has its own page: ISO Class 7.
One detail that merged tables hide: Annex 1 does not specify a 5 µm limit for Grade A in its classification table (Table 1), noting that 5 µm may be included where the contamination control strategy or historical trends indicate. Its monitoring table (Table 5) does set a Grade A limit of 29 particles per cubic metre at 5 µm, both at rest and in operation. A note to that table says occasional counts at 5 µm and above in Grade A may be false counts (electronic noise, stray light, coincidence loss), but consecutive or regular low counts “may be indicative of a possible contamination event and should be investigated.”
Where it matters for labs, clinics and supply decisions
ISO 5 conditions are typically delivered by unidirectional (laminar) airflow equipment, which is why the term turns up around hoods and isolators. Annex 1 gives a guidance air speed of 0.36 to 0.54 m/s at the working position for unidirectional systems unless otherwise scientifically justified, with airflow visualization studies expected to correlate. That airspeed is a separate expectation, not part of the class number. Equipment background is in what is a laminar flow hood. Clinics doing compounding should read USP <797> sterile compounding.
What an ISO Class 5 label does and does not tell you
| Question | What the sources say |
|---|---|
| Is the class a particle limit? | Yes. FDA Table 1 and Annex 1 Table 1 both express it as particles per cubic metre at 0.5 µm. |
| Does it cover microbes? | No. FDA lists microbiological expectations separately; ISO 5 areas should normally yield no microbiological contaminants. |
| Does it cover airflow speed? | No. Annex 1 gives 0.36 to 0.54 m/s as a separate guidance value. |
| When is it measured? | FDA: in the vicinity of exposed materials during activity. Annex 1: at rest and in operation, after a short clean-up period of under 20 minutes (guidance value) for the at-rest state. |
| Is Class 100 identical to Grade A? | FDA says approximately equal. |
Common misunderstandings
- “A whole room labelled ISO 5 is the norm.” FDA describes the ISO 5 critical area within a surrounding supporting area that is at least ISO 7 under dynamic conditions, though a filling room may be made entirely ISO 5.
- “Class 5 means a higher number is cleaner.” A lower ISO number is a stricter particle limit; ISO 5 is stricter than ISO 7 or ISO 8.
- “The 0.5 µm figure is the only number.” Annex 1 monitoring adds a 5 µm limit for Grade A.
- “Class 100 and Grade A are the same thing.” FDA’s own wording is “approximately equals.”
FAQ
What is the particle limit for ISO Class 5?
3,520 particles per cubic metre at 0.5 µm and larger, per FDA’s Table 1.
Is ISO Class 5 the same as Class 100?
FDA states an ISO 5 particle concentration is equal to Class 100, the legacy label.
Is ISO Class 5 the same as EU Grade A?
FDA says it approximately equals Grade A. Annex 1 Grade A has its own limits at rest and in operation, including a monitoring limit at 5 µm.
Sources
- U.S. Food and Drug Administration, Guidance for Industry: Sterile Drug Products Produced by Aseptic Processing: Current Good Manufacturing Practice, September 2004. https://www.fda.gov/media/71026/download (checked 2026-10-29).
- European Commission, EU GMP Volume 4, Annex 1 Manufacture of Sterile Medicinal Products, C(2022) 5938 final, 22 August 2022. https://health.ec.europa.eu/system/files/2022-08/20220825_gmp-an1_en_0.pdf (checked 2026-10-29).
