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The cleanroom's total enclosed volume.
Length × width × height of the space served by the HEPA supply filters.
How many times the room's full air volume is supplied per hour.
Typical industry design ranges by ISO 14644-1 class: ISO 8 ≈ 10-30 ACH, ISO 7 ≈ 30-65 ACH, ISO 6 ≈ 80-150 ACH, ISO 5 ≈ 200-480 ACH. These ranges come from IEST-RP-CC012.3 design guidance, not from ISO 14644-1 itself.
The combined open face area of all HEPA supply filters in the ceiling grid.
Used with the required airflow to check the resulting face velocity through the filter bank.
Required supply airflow
3,330 CFM
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
They open the calculator with your figures already in it
Cleanroom HEPA Airflow & Face Velocity Calculator: 3,333 CFM — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- 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).
Inputs used
- Cleanroom volume
- 2000 ft³
- Target Air Changes per Hour (ACH)
- 100
- Total HEPA filter face area
- 40 sq ft
Intermediate steps
- HEPA filter face velocity
- 83.33 ft/min
Confidence note: 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.
What this calculation does not cover
- This is total supply air, most of which is recirculated, and it says nothing about the outside air that holds the room positive against everything around it. The pressure cascade a cleanroom lives on — on the order of 5 to 15 Pa per classification step — is set by leakage through doors, pass-throughs and the envelope plus whatever process exhaust is drawn off, and a room supplied at exactly this rate with no offset loses its differential the first time a door swings.
- Air changes are a design input, not the acceptance result. The room is signed off on particle counts, and those depend on where the low-wall returns sit, how cleanly the air sweeps past benches and equipment, and how the space is gowned and operated — a room can hit this CFM exactly and still fail its classification because the supply short-circuits straight back to the ceiling.
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This result is a specification — 3,330 CFM — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- 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).
Which documents these citations point at
Standards referenced: ISO 14644-1 (International Organization for Standardization, International).
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