Cleanroom Air Changes Per Hour Calculator
Cleanroom ACH is the first number facilities and quality teams check when sizing a controlled environment for device assembly or packaging. Enter the room dimensions and supply flow to see how many times per hour the air is replaced and how many HEPA modules the target needs.
Your numbers
Set by your design basis, class and risk assessment. Values vary widely by ISO class.
Your results
Air change rate alone does not define cleanliness class. Classification and recovery depend on airflow pattern, filtration, particle sources and testing against your applicable standard.
Air changes per hour vs supply airflow
Sweeps Total supply airflow from 500 to 20000, holding your other inputs fixed.
Link environmental data to batches
Want cleanroom monitoring results tied to batch and lot records? We can review your options.
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How to use it
Enter room length, width and ceiling height, then the total supply airflow in cubic meters per hour. The calculator returns the volume and ACH. Enter the ACH your design basis requires to see the airflow you need, the shortfall and how many HEPA modules that implies at your module capacity. The chart shows how ACH scales with airflow so you can see the cost of reaching a higher rate.
The formula
Air changes per hour equals supply airflow per hour divided by room volume. A room of 144 cubic meters with 6,000 cubic meters per hour has about 41.7 ACH. Required airflow is the target ACH multiplied by volume, and modules are airflow divided by capacity, rounded up.
- ACH = airflow (m3/h) / volume (m3)
- Required airflow = ACH x volume
- Modules = ceiling of required airflow / module capacity
- Convert from cfm by multiplying by 1.699 to get m3/h
Common mistakes
Counting return or recirculated flow twice, or including fresh air only, gives the wrong ACH. Ceiling height should be the actual height to the ceiling plenum boundary, not the building height. High ACH does not guarantee a given class if the flow is turbulent, if there are internal particle sources or if filters leak. Rooms are classified by particle counts at rest and in operation, so use ACH for design sizing and rely on certification testing for compliance.
Frequently Asked Questions
What ACH does an ISO 7 room need?
There is no single mandated value. Design practice often falls in a range of tens of changes per hour, but the right figure depends on occupancy, activity, layout and recovery requirements. Set it from your design basis and verify by particle testing.
How do I convert cfm to m3/h?
Multiply cubic feet per minute by 1.699 to get cubic meters per hour. For example, 3,000 cfm is about 5,097 m3/h. Convert volume from cubic feet to cubic meters by multiplying by 0.0283.
Is ACH the same as cleanliness class?
No. Class is defined by airborne particle concentration limits measured in the room. ACH is one design input. Two rooms with the same ACH can test as different classes depending on airflow pattern and sources.
Does this include pressure cascades?
No. Room pressurization needs additional offset airflow calculated from leakage through doors and walls. Treat this tool as a first sizing step and let a facilities engineer complete the design.
If cleanroom monitoring and environmental records are kept in separate files, we can help tie them to batch records and ERP lots.
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