Cleanroom classes are defined by ISO 14644-1, which rates a room ISO 1 (cleanest) through ISO 9 by the maximum number of particles allowed per cubic meter; pharmaceutical GMP maps these to Grades A-D. The class you need is driven by your process – the tighter the class, the larger the HVAC/HEPA system behind it.
What are the different types of cleanroom classifications?
What are the different types of cleanroom classifications? Three systems are in active use and they are not interchangeable. ISO 14644-1 defines classes ISO 1 through ISO 9 by the maximum permitted particle count per cubic meter at specified particle sizes. EU GMP defines Grades A to D for pharmaceutical manufacture, adding requirements ISO 14644 does not cover, including microbiological limits and the distinction between at-rest and in-operation conditions. The superseded US FED-STD-209E defined Class 1 through Class 100,000 by particles per cubic foot, and although withdrawn it remains in everyday conversation — which is why “Class 100” is still heard far more often than “ISO 5”.
ISO 14644 cleanroom classes and GMP grades
| ISO Class | GMP Grade | Typical use |
|---|---|---|
| ISO 5 | Grade A / B | Aseptic fill-finish, sterile compounding |
| ISO 6 | – | Support around aseptic zones |
| ISO 7 | Grade C | Cleanroom background, non-sterile aseptic support |
| ISO 8 | Grade D | General GMP manufacturing, gowning |
| ISO 9 | – | Room air (uncontrolled) |
Lower ISO number = fewer allowable particles = more air changes, HEPA coverage, and monitoring.
How to choose the right class
Sterile injectables and aseptic processing need ISO 5 (Grade A) at the point of fill; oral solid dose and general GMP often run in ISO 8 (Grade D). Choosing a class tighter than your process requires wastes capital on HVAC you do not need.
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Frequently asked questionsWhat are the different types of cleanroom classifications?
There are three systems in active use. ISO 14644-1 classifies rooms ISO 1 to ISO 9 by maximum particle count per cubic meter at defined particle sizes, and is the international standard. EU GMP uses Grades A to D for pharmaceutical manufacturing and adds microbiological limits plus the at-rest and in-operation distinction that ISO 14644 does not itself impose. FED-STD-209E, the withdrawn US federal standard, used Class 1 to Class 100,000 based on particles per cubic foot and still survives in common speech, which is why people say Class 100 when they mean ISO 5.
>What is ISO 14644 and what does it govern?
ISO 14644 is the international standard family for cleanroom air cleanliness. Part 1 sets the airborne particle concentration limits that define each ISO class, and Part 2 covers the monitoring needed to demonstrate continued compliance. Paul Industries builds and certifies cleanrooms to these classes for cGMP manufacturers.
How many ISO 14644 cleanliness classes are there?
ISO 14644-1 defines nine classes, ISO Class 1 through ISO Class 9. Class 1 is the cleanest, permitting the fewest particles per cubic meter, while Class 9 is roughly equivalent to typical room air. Most pharmaceutical and biotech suites fall in the ISO 5 to ISO 8 range.
How does ISO 14644 map to the old Federal Standard 209E classes?
ISO Class 5 corresponds to the former Class 100, ISO Class 7 to Class 10,000, and ISO Class 8 to Class 100,000. Federal Standard 209E was withdrawn in 2001, so all new cleanroom specifications should reference ISO 14644 classes directly.
What particle sizes does ISO 14644-1 measure?
ISO 14644-1 sets limits at defined particle thresholds including 0.1, 0.2, 0.3, 0.5, 1, and 5 micrometers. The applicable sizes depend on the class; not every threshold is evaluated for every ISO class, which is why the classification report specifies which particle sizes were counted.
What is the difference between ‘at rest’ and ‘in operation’ classification?
‘At rest’ means the room is complete with equipment running but no personnel or production. ‘In operation’ means people and processes are active. ISO 14644 requires stating the occupancy state because particle counts rise sharply once operators and manufacturing generate contamination.
How often must an ISO 14644 cleanroom be recertified?
ISO 14644-2 ties monitoring frequency to the class. ISO Class 5 and cleaner typically require particle counting every 6 months, while ISO 6 through 9 rooms are often certified every 12 months. Airflow and pressure checks are performed more frequently under the monitoring plan.
What tests are required to classify a cleanroom to ISO 14644?
Particle counts at a defined number of sample locations determined by room area, taken in the occupancy state the specification names, which is the classification itself. Alongside it, the tests that show why the room performs: airflow velocity and volume, pressure differentials against the design cascade, and installed filter system leakage testing to confirm no bypass around seals or frames. Recovery testing and airflow visualization are separately defined and are worth specifying rather than assuming they are included.
How many sampling points does ISO 14644-1 require?
The number of sample locations is derived from the room’s floor area using the table in ISO 14644-1. Larger rooms require more points, and each location must meet the particle limit. The 2015 revision replaced the older square-root formula with a defined lookup approach.
What ISO class do most pharmaceutical fill lines need?
Aseptic filling zones are commonly ISO 5 at the point of fill, surrounded by an ISO 7 background and ISO 8 support areas. The exact grade depends on whether the product is terminally sterilized or aseptically processed, which Paul Industries confirms against the process before design.
How does ISO 14644 relate to EU GMP Grades A through D?
EU GMP Grades A and B correspond to ISO 5, Grade C to ISO 7, and Grade D to ISO 8 in the at-rest state. GMP adds microbial and in-operation limits that ISO 14644 does not, so a compliant suite must satisfy both frameworks together.
What causes a cleanroom to fail its ISO 14644 particle count?
Common causes include HEPA filter leaks, insufficient air changes, poor pressure cascade, worn gowning discipline, and particle-shedding materials or equipment. Paul Industries traces failures to root cause, corrects the deficiency, and re-runs the classification to demonstrate the room meets its ISO class.
Does ISO 14644 set a required air change rate?
No. ISO 14644 defines the particle limit, not the air change rate. The room designer selects an air change rate sufficient to hold the class in operation, often 20 to 60 changes per hour for ISO 7 and higher for cleaner grades, then verifies performance by particle counting.
What is HEPA filter integrity testing and is it part of ISO 14644?
HEPA integrity, or leak testing, uses an aerosol challenge and photometer scan to prove filters and their seals are intact. ISO 14644-3 describes the test methods. It is not part of the classification count itself but is essential to achieving and sustaining the ISO class.
Can Paul Industries certify our cleanroom to ISO 14644 nationwide?
Yes, nationwide, and certification is worth contracting deliberately rather than treated as a formality. What varies between providers is scope: whether recovery testing and envelope integrity testing are included, whether sampling locations follow the standard calculation or a convenient subset, and whether the report states the occupancy state tested. A certificate that does not name the occupancy state is close to meaningless, because a room that passes at rest can fail in operation.
What documentation proves ISO 14644 compliance?
A classification report identifies the occupancy state, tested particle sizes, sample locations, instrument calibration, measured counts, and the resulting ISO class with a pass or fail determination. This report, plus airflow, pressure, and filter records, forms the evidence auditors expect for cGMP cleanroom qualification.
What is the difference between classification and monitoring under ISO 14644?
Classification (Part 1) is the periodic test that assigns the ISO class. Monitoring (Part 2) is the ongoing routine sampling and data trending that demonstrates the room stays in control between classifications. A compliant program needs both, defined in a documented monitoring plan.
What are the cleanroom classes?
ISO 14644-1 classifies by the maximum permitted concentration of particles at or above specified sizes, per cubic meter of air. The scale runs from ISO 1, the cleanest, to ISO 9, which is roughly ordinary room air. Pharmaceutical work concentrates in ISO 5 through ISO 8. The class is defined at the particle size relevant to the application, so quoting a class without the size and the occupancy state is an incomplete specification.
What is the difference between ISO 5, ISO 7, and ISO 8?
Roughly two orders of magnitude between each step, and a much larger step in cost and energy. ISO 8 is achievable with a modest air change rate, often within an existing shell, at 150 to 365 dollars per square foot. ISO 7 needs a higher rate, a genuine pressure cascade and gowning airlocks, at 240 to 540. ISO 5 is the critical zone for aseptic operations, typically achieved with unidirectional flow over a small area rather than a whole room, at 700 to 1,650.
How do ISO classes map to GMP grades?
Approximately rather than exactly, and treating the mapping as exact causes trouble. EU GMP Grade A corresponds broadly to ISO 5 at rest and in operation, Grade B to ISO 5 at rest and ISO 7 in operation, Grade C to ISO 7 at rest and ISO 8 in operation, and Grade D to ISO 8 at rest with no defined in-operation limit. The substantive difference is that the EU grades carry associated microbiological monitoring limits, which ISO 14644 does not.
Which cleanroom class do I need?
The one your process actually requires, which is usually lower than the one first proposed. Aseptic processing needs ISO 5 at the critical zone with an ISO 7 background. Non-sterile pharmaceutical manufacture is commonly ISO 8. A great deal of laboratory, quality control and pilot work needs stable temperature, humidity and contamination control with no formal classification at all, and an unclassified controlled environment costs roughly half an ISO 8 room to build and carries no recurring certification.
Plan your cleanroom
Paul Industries is a single-source supplier, installer, and validator – one accountable partner from design through documented startup. Tell us about your project and we will scope it.
ISO 14644-1 particle limits: the full table
ISO 14644-1 classifies a cleanroom by the maximum permitted concentration of airborne particles per cubic meter at defined size thresholds. Each class is a tenfold reduction on the one below it.
| ISO class | ≥0.1 µm | ≥0.2 µm | ≥0.3 µm | ≥0.5 µm | ≥1.0 µm | ≥5.0 µm |
|---|---|---|---|---|---|---|
| ISO 1 | 10 | — | — | — | — | — |
| ISO 2 | 100 | 24 | 10 | 4 | — | — |
| ISO 3 | 1,000 | 237 | 102 | 35 | 8 | — |
| ISO 4 | 10,000 | 2,370 | 1,020 | 352 | 83 | — |
| ISO 5 | 100,000 | 23,700 | 10,200 | 3,520 | 832 | 29 |
| ISO 6 | 1,000,000 | 237,000 | 102,000 | 35,200 | 8,320 | 293 |
| ISO 7 | — | — | — | 352,000 | 83,200 | 2,930 |
| ISO 8 | — | — | — | 3,520,000 | 832,000 | 29,300 |
| ISO 9 | — | — | — | 35,200,000 | 8,320,000 | 293,000 |
The concentration limit for any class and particle size is given by Cn = 10N × (0.1 / D)2.08, where N is the ISO class number and D is the particle size in micrometers. Dashes above indicate combinations the standard does not classify, either because concentrations are impractical to measure or because the sample volume required is unreasonable.
ISO 14644 vs FED-STD-209E: the Class 100 equivalence
Most people still speak in FED-STD-209E class numbers — Class 100, Class 10,000 — even though the standard was superseded in 1999 and formally withdrawn in 2001. This is the mapping.
| ISO 14644-1 | FED-STD-209E | Particles ≥0.5 µm per m³ | Typical use |
|---|---|---|---|
| ISO 3 | Class 1 | 35 | Semiconductor lithography |
| ISO 4 | Class 10 | 352 | Advanced microelectronics |
| ISO 5 | Class 100 | 3,520 | Aseptic processing, open product exposure |
| ISO 6 | Class 1,000 | 35,200 | Aseptic support areas |
| ISO 7 | Class 10,000 | 352,000 | Sterile compounding support, device manufacture |
| ISO 8 | Class 100,000 | 3,520,000 | Component preparation, packaging |
How ISO classes map to EU GMP Grades A to D
This mapping causes more confusion than any other point in cleanroom classification, because a single EU GMP grade corresponds to two ISO classes — one at rest and a different one in operation.
| EU GMP grade | At rest | In operation | Microbial action limit |
|---|---|---|---|
| Grade A | ISO 5 | ISO 5 | <1 CFU/m³ |
| Grade B | ISO 5 | ISO 7 | 10 CFU/m³ |
| Grade C | ISO 7 | ISO 8 | 100 CFU/m³ |
| Grade D | ISO 8 | Not defined | 200 CFU/m³ |
An ISO classification is not a GMP grade. ISO 14644 addresses airborne particles only. EU GMP additionally imposes microbial limits, gowning, monitoring frequency and operational controls. A room can be correctly certified to ISO 7 and still fail Grade C.
The three classification states
| State | Equipment | Personnel | What it tells you |
|---|---|---|---|
| As-built | Installed, not operating | None present | The room envelope and air system work |
| At-rest | Installed and operating | None present | The room plus its equipment |
| Operational | Operating normally | Present and working | The only state that reflects production reality |
Classification reports must state which state was tested. A certificate that does not is not usable evidence — the same room will pass in one state and fail in another, and operational counts commonly run two to three times the at-rest figures.
Sampling: locations, volume and evaluation
- Number of sampling locations is the square root of the room area in square meters, rounded up: NL = ⌈√A⌉.
- Minimum sample volume per location must be enough to detect at least 20 particles at the class limit for the largest considered size: V = 20 / Cn,m × 1,000 liters, with a floor of 2 liters and at least 1 minute of sampling.
- Evaluation. Each location must meet the class limit. Where fewer than ten locations are sampled, the 95% upper confidence limit of the mean is also evaluated: UCL = mean + t × SD / √N.
- Failure. A failing location is investigated and corrected, then the affected locations are re-tested. A single failure does not automatically invalidate the whole room, but the investigation must be documented.
Air changes per hour: what the standard does and does not say
ISO 14644-1 does not specify air changes per hour. It specifies particle concentration outcomes. ACH is a design means of achieving them, which is why published ACH figures for the same class vary widely between sources — and why two of the most-cited cleanroom vendors contradict themselves across their own pages.
| ISO class | Typical design ACH range | Airflow pattern |
|---|---|---|
| ISO 8 | 10 – 30 | Turbulent / non-unidirectional |
| ISO 7 | 30 – 60 | Turbulent |
| ISO 6 | 90 – 180 | Turbulent, high filter coverage |
| ISO 5 | 240 – 480 | Often unidirectional, 0.36 – 0.54 m/s |
| ISO 4 and cleaner | Unidirectional throughout | Full ceiling coverage |
Treat these as design starting points, not requirements. The number that governs is the particle count, and the ACH needed to reach it depends on room geometry, headcount, equipment heat and particle generation, and filter coverage.
The other parts of ISO 14644
- ISO 14644-1 — Classification of air cleanliness by particle concentration
- ISO 14644-2 — Monitoring to provide evidence of continued performance, and requalification intervals
- ISO 14644-3 — Test methods, including filter integrity, airflow, pressure differential and recovery
- ISO 14644-4 — Design, construction and start-up
- ISO 14644-5 — Operations
- ISO 14644-7 — Separative devices: isolators, RABS, mini-environments
- ISO 14698 — Biocontamination control, which is where microbial limits live
Requalification intervals under ISO 14644-2 are commonly applied as a maximum of 6 months for ISO 5 and cleaner, and 12 months for ISO 6 and above — with immediate requalification triggered by significant changes to the room, the air system, the equipment or the process.
Size the airflow for a class
Once a target class is chosen, our cleanroom air change rate and HEPA calculator converts room dimensions into supply airflow, HEPA module count and low-wall returns, and checks whether that many filters physically fit the ceiling. Note the caveat it repeats from this page: the air change figures are industry design ranges used to reach a class, not requirements in ISO 14644-1, which classifies on measured particle counts.