Cleanroom classification tells you how strictly airborne particles must be controlled. Today, ISO 14644-1 is the primary international standard, while Class 1, Class 10, Class 100, Class 1,000, Class 10,000, and Class 100,000 are legacy classifications from the former U.S. Federal Standard 209E.
Understanding these classifications helps determine the level of air cleanliness a process requires. This guide explains Class 1 through Class 100,000, their corresponding ISO classes, particle limits, typical applications, and key considerations for selecting the right cleanroom.
Cleanroom Classification Chart
The following chart shows the legacy FS 209E classes alongside the corresponding ISO classes based on the maximum concentration of particles measuring 0.5 micrometers (µm) and larger.
| Legacy Cleanroom Class | ISO Class | Maximum Particles ≥0.5 µm/m³ |
| Class 1 | ISO 3 | 35 |
| Class 10 | ISO 4 | 352 |
| Class 100 | ISO 5 | 3520 |
| Class 1,000 | ISO 6 | 35,200 |
| Class 10,000 | ISO 7 | 352,000 |
| Class 100,000 | ISO 8 | 3,520,000 |
These values show the maximum particle concentration at 0.5 μm and larger for the listed ISO classes. They do not define temperature, humidity, pressure, microbial contamination, surface contamination, or chemical contamination. Those requirements must be established separately when they affect the product or process.
Class 1 Cleanroom – ISO Class 3
At ISO Class 3, no more than 35 particles measuring 0.5 µm and larger are allowed per cubic meter of air.
This low particle limit is used for processes that can be affected by very small amounts of airborne contamination. Examples include some semiconductor production steps, nanotechnology work, precision optics, and specialized research.
Keeping particle counts this low requires effective filtration and carefully controlled airflow. Filtered air removes particles released by people, equipment, and activities inside the room. Some processes use air that moves in one direction across the work area to carry particles away from sensitive products and surfaces.
Typical gowning may include:
- Full cleanroom coverall or suit
- Hood
- Cleanroom gloves
- Face covering or mask when needed
- Cleanroom boots or dedicated footwear
People and materials can introduce particles every time they enter the room. Entry procedures, cleaning, material transfer, and personnel movement must therefore be carefully managed.
Class 1 is intended for processes that need very low airborne particle counts. Choosing this class when it is not necessary can increase filtration, energy, testing, and operating costs without providing a useful benefit to the process.
Class 10 Cleanroom – ISO Class 4
A Class 10 cleanroom has a limit of 352 particles measuring 0.5 µm and larger per cubic meter under ISO Class 4.
This class can be used for certain semiconductor, microelectronics, precision optics, and research processes. In these applications, particles that settle on exposed components or surfaces can cause defects or affect performance.
The air system supplies filtered air while removing air that carries particles generated inside the room. Some sensitive work areas may also use airflow that moves in one direction, helping keep airborne particles away from exposed products.
Typical gowning may include:
- Full cleanroom coverall
- Hood
- Cleanroom gloves
- Face covering when needed
- Cleanroom boots or dedicated footwear
Filtration alone cannot control every source of contamination. People, tools, equipment, packaging, and materials can all introduce particles. Cleaning, entry procedures, and material handling must work together with the air system to maintain the required particle level.
Class 100 Cleanroom – ISO Class 5
For Class 100 / ISO Class 5, the maximum concentration is 3,520 particles measuring 0.5 µm and larger per cubic meter.
This class is used for certain semiconductor and electronics processes, precision optics, medical-device manufacturing, biotechnology, and pharmaceutical operations. It may be selected when airborne particles could affect the product or interfere with the process.
In some facilities, only the most sensitive work area needs ISO Class 5 conditions. For example, filtered air may flow directly over an exposed product or work surface to keep airborne particles away. The rest of the room can use a different cleanroom class if the process and industry requirements allow it.
This arrangement places the cleanest air around the work that needs the most protection instead of requiring the entire room to meet the same particle limit.
Typical gowning may include:
- Cleanroom coverall
- Hood or hair covering
- Cleanroom gloves
- Face mask when needed
- Cleanroom boots or dedicated footwear
The exact gowning depends on the work being performed. Pharmaceutical production may require more body coverage because workers can release particles and microorganisms from their skin, hair, and clothing. Electronics manufacturing may use different clothing when the main concern is keeping particles away from sensitive components.
The gowning procedure should therefore be based on the contamination risks of the process rather than the ISO class alone.
Class 1,000 Cleanroom – ISO Class 6
A Class 1,000 cleanroom has a maximum limit of 35,200 particles measuring 0.5 µm and larger per cubic meter under ISO Class 6.
This class can be used for certain electronics, optical components, medical devices, precision parts, and laboratory work. It allows more airborne particles than ISO Class 5 but fewer than ISO Class 7.
An ISO Class 6 room can also be used around a smaller ISO Class 5 work area. In this setup, the ISO Class 5 area protects the most sensitive part of the process, while the surrounding ISO Class 6 room helps reduce the amount of contamination that can reach it.
The amount of filtered air needed depends on how the room is used. More workers, equipment that releases particles, frequent door openings, and active production can all increase the particle load inside the room. The air system must remove enough of these particles to keep the room within the required limit.
Typical gowning may include:
- Cleanroom coverall or suit
- Hair covering or hood
- Cleanroom gloves when needed
- Shoe covers or dedicated cleanroom footwear
There is no single air-change rate that applies to every ISO Class 6 cleanroom. The required airflow depends on the room size, number of people, equipment, particle sources, and activities taking place inside the space.
Class 10,000 Cleanroom – ISO Class 7
Under ISO Class 7, a Class 10,000 cleanroom can contain up to 352,000 particles measuring 0.5 µm and larger per cubic meter. This class is used in certain manufacturing areas, electronics assembly, laboratories, pharmaceutical support areas, and precision manufacturing.
Filtered air removes particles released by workers, equipment, and normal production activities. The room may also be kept at a different air pressure from the nearby spaces. When a pressure difference is needed, it helps control the direction in which air moves between rooms and reduces the chance of contamination entering a cleaner area.
Typical gowning may include:
- Cleanroom overall, frock, or dedicated garment
- Hair covering
- Cleanroom gloves when needed
- Shoe covers or dedicated cleanroom footwear
Daily activity has a direct effect on particle levels. Opening doors, moving materials, operating equipment, and walking around the room can release or carry particles. Cleaning methods, staff movement, and material handling all play a role in keeping the room within its particle limit.
A well-designed ISO Class 7 room can still exceed its particle limit if it is not operated and maintained correctly.
Class 100,000 Cleanroom – ISO Class 8
At ISO Class 8, the maximum concentration rises to 3,520,000 particles measuring 0.5 µm and larger per cubic meter. This class is used for certain medical-device processes, electronics work, laboratories, packaging, controlled production and support areas next to cleaner rooms.
An ISO Class 8 room can also serve as a controlled area between an unclassified space and a cleaner room. For example, workers may pass through an ISO Class 7 room. This helps reduce the amount of contamination carried toward the cleaner space.
Typical gowning may include:
- Cleanroom coat, frock, or coverall
- Hair covering
- Shoe or dedicated footwear
- Cleanroom gloves when needed
Filtered air, regular cleaning, staff practices, and material handling all help keep particle levels within the required limit. HEPA filters are often used in cleanrooms, but installing a HEPA filter does not automatically give a room an ISO classification. Particle testing must confirm that the room meets the required limit.
Class 100,000 allows more airborne particles than other classes. If this class meets your process requirements, choosing a cleaner class will increase equipment, energy, testing, and operating costs without adding necessary protection.
Does ISO Class Determine Air Changes Per Hour?
No. ISO 14644-1 does not assign a specific air changes per hour (ACH) rate to each cleanroom class. The amount of airflow needed depends on the room size, number of workers, equipment, particle sources, and activities inside the room.
A busy production area may need more filtered air than a room with fewer people and less activity, even if both rooms have the same ISO classification. ACH can be used when designing the ventilation system, but the final requirement is to keep airborne particle levels within the specified class.
At-Rest vs. Operational Cleanroom Classification
A cleanroom can be classified at rest or operational, and the difference is important when evaluating particle levels. An at-rest cleanroom has its equipment installed and operating as specified, but normal production is not taking place.
An operational cleanroom is tested while the specified workers, equipment, and processes are active. Particle counts are often affected by normal work. Workers move around, doors open, materials enter the room, and equipment operates.
A room that meets its particle limit at rest may therefore have different particle levels during production. The cleanroom specification should clearly state which condition applies when the room is classified.
How Is a Cleanroom Classification Verified?
Cleanroom classification is verified by measuring airborne particle concentrations. A particle counter collects a known volume of air and measures particles at selected sizes. Samples are taken at specified locations throughout the room and compared with the limits for the required ISO class.
Testing several locations is necessary because particles may not be evenly distributed throughout the space. Installing HEPA filters or designing a room for a certain ISO class does not prove that the room meets that class. The required particle limit must be confirmed through testing.
Test records should identify the ISO class, particle size used for classification, sampling locations, and whether the room was tested at rest or during operation.
How to Choose the Right Clean Room Class
The right cleanroom class depends on how sensitive the product or process is to airborne contamination. Start by identifying the particles that could affect the work. Then consider where those particles may come from, such as workers, equipment, materials, packaging, or the production process.
The room should be designed to maintain the required particle level during the conditions in which it will normally operate. Other environmental requirements may also need to be considered. Depending on the application, these can include temperature, humidity, pressure, microorganisms, surface contamination, and chemical contamination. These controls are separate from the ISO airborne particle classification.
Choosing a cleaner class than the process requires can increase construction, filtration, energy, cleaning, testing, and maintenance costs. Choosing a class that allows too many particles may leave the product or process without enough protection.
The goal is therefore not to choose the lowest ISO class number. It is to choose the particle limit that matches the needs of the process.
Conclusion
The right cleanroom class depends on the product and the amount of airborne contamination that needs to be controlled. Choosing a cleaner class than necessary can increase costs, while choosing a class with too little particle control can put the product or process at risk. A cleaner room also depends on good airflow, filtration, temperature control, and proper daily operation. These factors should be planned together so the room can maintain the required conditions during use.
If you are planning a cleanroom and are unsure which classification is right for your application, Sunnyda Clean Room can help. Whether you have questions about particle limits, room design, or choosing the right cleanroom class, our team can discuss your requirements and help you find a solution that fits your process.
Frequently Asked Questions
What is a Class 1 cleanroom?
Class 1 is an older FS 209E classification. At 0.5 µm, its particle level is comparable to ISO Class 3, which allows up to 35 particles per cubic meter.
What is a Class 100 cleanroom?
Class 100 is the older term for a particle level comparable to ISO Class 5 at 0.5 µm. ISO Class 5 allows up to 3,520 particles per cubic meter.
What is a Class 1,000 cleanroom?
Class 1,000 is comparable to ISO Class 6 at 0.5 µm, with a limit of 35,200 particles per cubic meter.
What is a Class 10,000 cleanroom?
Class 10,000 is comparable to ISO Class 7 at 0.5 µm. ISO Class 7 allows up to 352,000 particles per cubic meter.
What is a Class 100,000 cleanroom?
Class 100,000 is comparable to ISO Class 8 at 0.5 µm, which allows up to 3,520,000 particles per cubic meter. Does cleanroom classification determine gowning requirements?
Does cleanroom classification determine gowning requirements?
No. ISO 14644-1 does not specify what workers must wear for each cleanroom class. Gowning requirements depend on the product, process, contamination risks, industry requirements, and facility procedures. The gowning lists provided for each class in this guide are typical examples, not requirements set by ISO 14644-1.
Does a HEPA filter determine the cleanroom class?
No. HEPA filtration helps remove airborne particles, but the cleanroom class is determined by the particle concentration measured during testing. Installing HEPA filters alone does not give a room a particular ISO classification.
You may also find these blog posts useful:
Cleanroom Environmental Monitoring Systems: A Comprehensive Guide
What is the Difference between Sterile and Clean in a Cleanroom?
What’s the Difference between a Controlled Environment and a Cleanroom?
