Online Tools

    Ventilation Calculator

    Calculate room ventilation airflow in CFM, air changes per hour (ACH), current ACH and a rough round duct diameter from room volume.

    Formula: ACH = CFM × 60 ÷ room volume, so CFM = room volume × target ACH ÷ 60. If occupants are entered, recommended CFM is the larger of the ACH airflow and 15 CFM per person.

    Use this as a planning estimate. Code ventilation, combustion safety, pressure balance and duct losses need HVAC review.

    Calculate CFM from ACH

    English ventilation-calculator intent centers on CFM and ACH. Enter room dimensions in feet, choose a target air-change rate, and compare required airflow with an optional current fan CFM.

    ACH — air changes per hour, CFM — cubic feet per minute, V — room volume in cubic feet.

    CFM — required airflow, V — room volume in cubic feet, ACH — target air changes per hour.

    V — room volume, L — length, W — width, H — ceiling height.

    Planning limits

    • ACH is useful for room-level estimates but does not prove code compliance by itself.
    • Outdoor air, recirculated filtration and equivalent clean air are not the same for every pollutant.
    • Duct losses, fan curves, static pressure, noise, pressure balance and combustion safety are outside this estimate.
    • Bathrooms, kitchens, classrooms, labs and commercial spaces can have specific local code requirements.
    HVAC review required
    Use this as a sizing estimate. A real ventilation design must check local code, outdoor-air requirements, filtration, duct losses, moisture and system balance.

    Frequently Asked Questions

    Sources and References

    Calculations are based on the listed reference sources. Links open in a new tab.

    Updated:

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