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Cleanroom HEPA Airflow & Face Velocity Calculator

Calculate the required supply airflow and HEPA filter face velocity for a cleanroom, based on a target air-changes-per-hour rate by ISO class.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Required supply airflow

3333.33 CFM

Check your inputs

The ACH-by-ISO-class ranges are industry design guidance (IEST-RP-CC012.3), not an ISO 14644-1 requirement — ISO 14644-1 itself only sets particle-concentration limits, not airflow rates. Final design ACH depends on process particle generation, occupancy, and equipment heat load, and should be verified by the project's cleanroom design engineer. ISO 5 spaces are often designed as unidirectional/laminar flow at a target face velocity instead of a pure ACH value.

HEPA filter face velocity
83.33 ft/min

For the dimensions entered, expect a required supply airflow of 3333 CFM. Note that cleanroom volume (ft³) sits at the low end of the range this calculator was checked against, so treat the output as indicative rather than settled. Moderate confidence — sound arithmetic, but allow for the variation any real site introduces. Set for United States against IRC 2024. The market selector changes both the units and the code cited.

Add the equipment this sizes

This result is a specification — 3,333.333 CFM — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Required airflow (CFM) = Room Volume (ft³) × Air Changes per Hour ÷ 60; Face Velocity (ft/min) = Airflow ÷ HEPA Filter Face Area. Typical ACH design ranges by ISO 14644-1 cleanliness class come from secondary design guidance (IEST-RP-CC012.3 'Considerations in Cleanroom Design' and established industry practice, NOT from ISO 14644-1 itself, which sets only particle-concentration limits): roughly ISO 8 → 10-30 ACH, ISO 7 → 30-65 ACH, ISO 6 → 80-150 ACH, ISO 5 → 200-480 ACH (ISO 5 is often instead designed as unidirectional/laminar flow at ~40-80 fpm face velocity rather than a pure ACH target).

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Frequently asked questions

How is the required cleanroom airflow calculated?
Required airflow (CFM) equals the room's volume in cubic feet multiplied by the target air changes per hour (ACH), divided by 60 minutes — the same room-volume-times-ACH method used for general ventilation, applied here to cleanroom HEPA supply.
Where do the typical ACH ranges by ISO class come from?
They come from secondary design guidance such as IEST-RP-CC012.3 and established industry practice — not from ISO 14644-1 itself, which only sets particle-concentration limits and does not specify airflow rates. Roughly: ISO 8 → 10-30 ACH, ISO 7 → 30-65 ACH, ISO 6 → 80-150 ACH, ISO 5 → 200-480 ACH.
Why does the result also show a face velocity?
Face velocity (airflow ÷ total HEPA filter face area) confirms the filter bank size is adequate for the required airflow. ISO 5 spaces are often instead designed directly as unidirectional/laminar flow at a target face velocity (roughly 40-80 ft/min) rather than a pure ACH target, so final design ACH and face velocity should always be verified by the project's cleanroom design engineer.