📊 Target ACH
📈 Cascade Pressure
Design Breakdown
Full Calculation Table
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How to Use the Clean Room Calculator
Choose the target ISO 14644-1 classification for the room, from ISO Class 5, the cleanest tier covered here, to ISO Class 8, the least restrictive.
Enter length, width, and ceiling height to calculate room volume, which the air change rate scales against.
Enter how many anterooms or airlocks sit between this room and the general corridor. Each one adds a pressure step to the cascade estimate.
Click Calculate Airflow to see the design ACH, supply airflow and its typical range, and the pressure cascade for your room.
Clean Room Airflow by ISO 14644-1 Class
Clean room classes are set by particle counts, not by airflow. Air changes per hour is the practical design tool used to reach and hold a class, and this calculator turns it into a supply airflow for your room. The 6 m by 4 m by 2.7 m example room is 64.8 m³. At 75 ACH, the ISO Class 7 design value, it needs 64.8 × 75 ÷ 3.6 = 1,350 L/s (about 2,860 CFM).
Typical ACH Ranges
ISO 14644-1:2015 classifies air cleanliness by the concentration of airborne particles. It sets no airflow, so the ranges below come from engineering guidance and differ from one source to the next. Commonly quoted figures are 240 to 480 ACH for ISO Class 5 (some sources go to 600), 90 to 240 for Class 6, 60 to 90 for Class 7 (some go to 150), and 5 to 48 for Class 8 (some go to 60). The calculator designs near the middle of each range, at 360, 165, 75 and 25 ACH, and shows the range as a low and a high airflow. ISO Class 5 is normally built with unidirectional, near-laminar flow and sized by face velocity across a HEPA ceiling, so its ACH is only a rough equivalent.
Why Pressure Cascade Matters
A clean room only stays clean if air moves from cleaner spaces toward less clean ones every time a door opens. FDA's aseptic processing guidance calls for a positive pressure differential of at least 10 to 15 Pa between adjacent rooms. This calculator uses 12.5 Pa per step. Count steps, not rooms: a clean room with one anteroom has two steps, room to anteroom and anteroom to corridor, so it holds about 25 Pa over the corridor. Use the space pressurization calculator to check the supply and return imbalance needed to hold each step, and the makeup air calculator if the cascade needs dedicated outside air to maintain.
Related Controlled Environments
Hospital operating rooms and isolation rooms use a similar ACH-driven design logic with their own targets under CSA Z317.2 and ASHRAE 170, which the hospital ventilation calculator covers directly. Laboratory spaces with fume hoods follow a related but distinct logic driven by hood exhaust rather than a flat ACH target, covered in the laboratory ventilation calculator. For the commercial HVAC side of a cleanroom project, there is also a cleanroom HVAC calculator.
Filtration and Makeup Air
ISO Class 5 through 7 spaces almost always need HEPA filtration, typically at the terminal supply diffuser, and the high air change rates involved mean recirculated air usually dominates over fresh outdoor air. The HEPA filter calculator is a useful check on the filtration side. Whatever outdoor air the space does need still has to be made up somewhere, so check that the air handling system has enough fresh air capacity using the outside air calculator alongside this tool.
Frequently Asked Questions
Commonly cited design guidance is 60 to 90 air changes per hour for an ISO Class 7 clean room with non-unidirectional, mixed flow, and some sources run as high as 150. This calculator uses 75 ACH as its design value. The right number depends on particle sources, occupancy and process equipment, so treat it as a starting point for design, not a value from the ISO 14644-1 standard.
No. ISO 14644-1 classifies air cleanliness by the concentration of airborne particles and does not set an airflow rate. Air changes per hour is the design practice used to reach and hold a class, and the ranges come from engineering guidance, so published figures differ from one source to the next. That is why this calculator shows a typical range beside its design value.
FDA's aseptic processing guidance says a positive pressure differential of at least 10 to 15 Pa should be maintained between adjacent rooms. This calculator uses 12.5 Pa per step, and each anteroom or airlock adds a step, so a room with one anteroom has two steps and about 25 Pa to the corridor. Door swing, airlock design and the cleanliness classes involved all affect the real target, so confirm it with a qualified design engineer. The space pressurization calculator can help check the supply and return airflow needed.
ISO Class 5 through 7 spaces almost always need HEPA filtration, often at the terminal supply diffuser, to achieve the required particle counts. ISO Class 8 spaces can sometimes use a combination of HEPA and high-efficiency pre-filtration depending on the application. Filter selection should be confirmed against the specific process and any applicable Health Canada or GMP requirements for pharmaceutical and medical device spaces.