Choosing between ISO Class 5, 6, 7, and 8 starts with one question: how much airborne particulate contamination can your process tolerate? The difference is significant. At particles ≥0.5 µm, each step from ISO 5 to ISO 8 allows ten times the particle concentration of the previous class.
But particle limits are only part of the decision. Your product, process, equipment, personnel, and applicable regulations determine which class is appropriate. This guide compares ISO cleanroom Classes 5–8, their particle limits, key differences, testing conditions, and the factors you should consider before specifying a cleanroom.
What Do ISO Cleanroom Classes 5-8 Mean?
ISO Classes 5-8 define different levels of airborne particle cleanliness under ISO 14644-1. The lower the class number, the fewer airborne particles are permitted. At particles ≥0.5 µm, the limit ranges from 3520 particles/m3 for ISO 5 to 3,520,000 particles for ISO 8.
ISO classification is based on airborne particle concentration. It does not assign one fixed temperature or humidity level, air change rate, or cleanroom design to each class.
ISO Class 5-8 Particle Limits
The table below shows the maximum permitted particle concentrations for ISO Classes through 8. All values are particles per cubic meter of air.
| ISO Class | ≥0.1 µm | ≥0.2 µm | ≥0.3 µm | ≥0.5 µm | ≥1 µm | ≥5 µm |
Legacy FS 209E name
|
| ISO 5 | 100,000 | 23,700 | 10,200 | 3,520 | 832 | N/A | Class 100 |
| ISO 6 | 1,000,000 | 237,000 | 102,000 | 35,200 | 8,320 | 293 | Class 1,000 |
| ISO 7 | N/A | N/A | N/A | 352,000 | 83,200 | 2,930 | Class 10,000 |
| ISO 8 | N/A | N/A | N/A | 3,520,000 | 832,000 | 29,300 | Class 100,000 |
Not every particle size has a specified limit for every ISO class. N/A indicates that ISO 14644-1 does not specify a classification limit for that particular particle size and class. You may still encounter older terms Class 100, Class 1,000, Class 10,000, and Class 100,000. These come from the former U.S. Federal Standard 209E.
For current specifications, using the applicable ISO class provides clearer terminology.
ISO Class 5, 6, 7, and 8: Where Does Each Class Fit?
The particle limits tell you the measurable difference between ISO 5-8. In practice, the more useful question is where each class fits and what you need to consider when designing the space.
What Is an ISO Class 5 Cleanroom?
ISO Class 5 is commonly associated with processes where airborne particles can directly affect a sensitive product or critical operation. Applications may include certain aseptic pharmaceutical processes, semiconductor manufacturing, biotechnology, and precision production.
The challenge is maintaining the required conditions where the critical work actually happens. Equipment placement, airflow around the process, operator activity, material transfer, and particle-generating operations all need attention. In some facilities, ISO 5 conditions are needed only around a critical process rather than throughout an entire room.
What Is an ISO Class 6 Cleanroom?
ISO Class 6 can be specified when a process needs a defined level of particle control that falls within its ISO 14644-1 limits. Applications vary because the classification should come from the process requirement rather than an industry label. It may be used for sensitive manufacturing, assembly, or processing where controlling airborne particles is important to product quality.
When planning an ISO 6 space, consider where particles are generated and how they move. Operators, equipment, work surfaces, material transfer, and airflow can all influence actual room performance.
What Is an ISO Class 7 Cleanroom?
ISO Class 7 is widely used for manufacturing processes that require a controlled airborne environment. Depending on the product and applicable requirements, examples can include medical device manufacturing, pharmaceutical operations, electronics, laboratories, and precision assembly.
For ISO 7 projects, room classification is only one part of the specification. Equipment heat loads, personnel activity, material flow, pressure relationships, temperature, humidity, and recovery requirements can influence the final design. This is why two ISO 7 cleanrooms may have very different layouts and environmental-control systems.
What Is an ISO Class 8 Cleanroom?
ISO Class 8 is commonly used where a process needs controlled airborne cleanliness but does not require the environmental conditions associated with more contamination-sensitive operations. Applications can include certain manufacturing, assembly, preparation, packaging, and support areas.
The main design question is what needs to be controlled for the actual process. Particle sources, personnel movement, incoming materials, equipment, cleaning procedures, temperature, humidity, and pressure may still matter even when the room meets its ISO 8 particle limits.
An ISO 8 specification should therefore be based on the needs of the operation rather than the classification number alone.
How Do You Choose Between ISO 5, 6, 7, and 8?
Choose the class according to your product sensitivity, process exposure, regulatory requirements, equipment, personnel, and operating conditions.
Ask these questions:
- How sensitive is the product to particles?
- Is the product exposed directly to room air?
- Do regulations or customer requirements specify a class?
- How many people will work in the room?
- Can equipment generate particles or disturb airflow?
- How often will materials enter and leave?
- Under what operating state must the room meet its classification?
- Are temperature, humidity, or pressure critical to the process?
Not every part of a facility needs the same classification. Where the process allows it, a cleaner critical zone can operate within a less strict background environment. This concentrates contamination control where it is needed instead of over-specifying the entire facility.
What Does ISO Class Tell You About Cleanroom Design?
An ISO class tells you the required airborne particle cleanliness. It does not provide a complete cleanroom design. ISO 14644-1 does not assign a universal air-change rate, temperature, humidity range, pressure differential, or gowning system to ISO Classes 5-8.
The design still needs to account for airflow, filtration, equipment, heat loads, personnel, material movement, pressure relationships, and process conditions.
This is why two ISO Class 7 cleanrooms can have different HVAC systems and layouts while still meeting the same particle classification.
Is Air Changes per Hour the Same as ISO Class?
No. ISO class and air changes per hour (ACH) measure different things. ISO class is based on airborne particle concentration. ACH describes the volume of supplied air relative to room volume over one hour.
ISO 14644-1 does not assign one universal ACH value to each class. The required airflow depends on the room, process, occupancy, particle source, equipment, and performance requirements.
How Is an ISO Cleanroom Classified?
A cleanroom is classified by measuring airborne particle concentrations at designated sampling locations and comparing the results with ISO 14644-1 limits. The conditions during testing must also be defined. Common occupancy states include:
As-Built
The cleanroom installation is complete and operating, but production equipment, materials, and personnel are not present.
At-Rest
Equipment is installed and operating under agreed conditions, but personnel are not carrying out normal production work.
Operational
The cleanroom is functioning under defined operating conditions with the specified personnel performing their work. Occupancy matters because people, equipment, materials, and door activity can change particle concentrations. When reviewing a test result, check both the ISO class achieved and the occupancy state used for classification.
How Do ISO Classes Compare with EU GMP Grades?
EU GMP grades and ISO cleanroom classes are related, but they are not interchangeable. ISO 14644-1 classifies airborne particle cleanliness. EU GMP Annex 1 applies to sterile medicinal-product manufacturing and includes broader contamination-control requirements.
For particle concentrations, the commonly referenced relationships are:
| EU GMP Grade | At Rest | In Operation |
| Grade A | ISO 5 particle limits | ISO 5 particle limits |
| Grade B | ISO 5 particle limits | ISO 7 particle limits |
| Grade C | ISO 7 particle limits | ISO 8 particle limits |
| Grade D | ISO 8 particle limits | Defined according to risk |
These relationships concern particle limits only. For example, meeting ISO 5 particle limits does not by itself demonstrate compliance with all EU GMP Grade A requirements. For non-pharmaceutical projects, GMP grades may not apply.
Can Equipment Affect Cleanroom Classification?
Yes. Operating equipment can generate particles or disturb airflow. Motors, bearings, conveyors, moving parts, tools, friction, and wear can contribute to particle generation.
ISO 14644-14:2026 provides a methodology for assessing equipment suitability with respect to airborne particle cleanliness. Equipment should therefore be considered under realistic operating conditions, not only when it is switched off.
What Happens If a Cleanroom Fails a Particle Test?
First, confirm the test conditions and where the elevated particle count occurred. Possible causes include HEPA filter leakage, poor airflow, blocked returns, equipment, personnel activity, cleaning or gowning problems, frequent door opening, and recent maintenance.
A localized high count may indicate a different problem from elevated concentrations throughout the room. Find and correct the cause, then perform the appropriate retesting.
Does Passing Classification Mean the Cleanroom Will Stay Compliant?
No. Classification confirms airborne particle cleanliness under defined conditions at the time of testing. Performance can change as filters age, equipment wears, and production conditions change.
ISO 14644-2 specifies minimum requirements for a monitoring plan related to air cleanliness by particle concentration. Monitoring helps provide evidence of continued cleanroom performance.
What Should You Tell a Cleanroom Supplier?
Give the supplier enough information to understand the process behind the ISO class.
Key information includes:
- Target ISO class
- Product and process
- Applicable regulatory requirements
- Room size and layout
- Number of operators
- Production equipment and heat loads
- Temperature and humidity requirements
- Pressure requirements
- Personnel and material flow
- Operating schedule
- Required classification state
- Future production or expansion needs
An ISO class alone is not a complete cleanroom specification. Two ISO Class 7 projects can require very different designs because their processes, equipment, and environmental requirements differ.
Conclusion
Choosing between ISO Class 5, 6, 7, and 8 should start with your process, product sensitivity, operating conditions, and applicable requirements. The ISO class sets the airborne particle target, while the cleanroom design determines how that target is achieved and maintained.
If you have any questions about cleanroom classification or need a cleanroom for your project, Sunnyda Clean Room can help you determine the right solution for your application.
Frequently Asked Questions
Is ISO Class 7 suitable for medical device manufacturing?
It can be. ISO Class 7 is used for medical device manufacturing processes, but the required classification depends on the device, production process, contamination risk, and applicable regulatory requirements.
Does a lower ISO class number mean a cleaner room?
Yes, specifically for airborne particle concentration. A lower ISO class permits fewer airborne particles at the particle sizes specified by ISO 14644-1.
Can one facility have different ISO cleanroom classes?
Yes. Different rooms or clean zones can have different classifications based on the contamination control needs of each process or area.
How often should a cleanroom be tested?
The appropriate testing and monitoring schedule depends on the applicable ISO standard and requirements, your monitoring plan, process risk, and any industry-specific regulations. Classification should not be treated as a one-time indication of future performance.
Can an existing cleanroom be upgraded to a different ISO class?
Yes, in some cases. The existing airflow, filtration, room construction, equipment, and contamination sources should first be evaluated to determine what changes are required.
Does an ISO cleanroom need HEPA filters?
HEPA filtration is commonly used in cleanrooms to control airborne particles. The filtration system should be selected and designed around the required cleanliness level and process conditions.
