Estimates the cubic-feet-per-minute (CFM) airflow a fan or HVAC system needs to achieve a target number of full air changes per hour in a room.
How it works
The room’s volume is multiplied by the target air changes per hour, then divided by 60 to convert from an hourly to a per-minute rate.
What this does not include
This does not include duct sizing or static pressure calculations — this calculator specifically estimates the required airflow rate.
How to use this calculator
- Enter the room’s volume in cubic feet and the target air changes per hour.
A worked example
A 1,000 cubic foot room needing 4 air changes per hour (ACH): CFM = (volume × ACH) ÷ 60 = 66.6667 CFM.
A 2,000 cubic foot room at 6 ACH: CFM = 200.
What the variables mean
| Variable | Meaning |
|---|---|
| Volume | Room volume, in cubic feet |
| ACH | Desired air changes per hour |
Edge cases worth knowing
CFM scales directly with both room size and desired air-change rate — doubling either one doubles the required CFM, which is why larger rooms or higher ventilation standards need proportionally bigger fans.
Zero ACH makes the required CFM zero, a valid but trivial result the calculator declines to show since it implies no ventilation is wanted at all.
Frequently asked questions
What’s a typical air changes per hour (ACH) target?
It varies by room type — bedrooms typically target 4-6 ACH, while kitchens and bathrooms often need 8-15+ due to moisture, heat, or odor.
How do I find a room’s volume?
Multiply its length, width, and height (all in feet) to get cubic feet.
Why does a kitchen need more air changes than a bedroom?
Kitchens generate more heat, moisture, and airborne particles from cooking, requiring faster air turnover to keep the space comfortable and safe.
