CFM Calculator
Calculate airflow in cubic feet per minute from room size and air changes per hour, or from duct size and air velocity.
Airflow
144 cubic feet per minute
- Cubic meters per hour
- 245 m³/h
- Cubic feet per hour
- 8,640
A room of 1,440 cubic feet changed 6 times an hour needs 144 CFM of airflow, which is 244.7 cubic meters per hour.
Calculation breakdown
| Step | Formula | Result |
|---|---|---|
| Room volume | 15 × 12 × 8 | 1,440.0 ft³ |
| Airflow | 1,440 ft³ × 6 ÷ 60 | 144.0 CFM |
How it works
Choose a room or a round duct. For a room, enter its size and the air changes per hour. For a duct, enter its diameter and the air velocity.
Worked example
A room 15 ft long, 12 ft wide and 8 ft high with 6 air changes an hour:
- Volume: 15 × 12 × 8 = 1,440 cubic feet
- Airflow: 1,440 × 6 ÷ 60 = 144 CFM
- In metric: 144 × 60 × 0.0283168 = 245 cubic meters per hour
Rounding
Airflow is shown to the nearest whole CFM. Calculations use the unrounded values.
Sources
Frequently asked questions
How do you calculate CFM for a room?
Multiply the room volume in cubic feet by the air changes per hour you want, then divide by 60. A room of 15 by 12 feet with an 8 foot ceiling is 1,440 cubic feet, and 6 air changes an hour needs 1,440 × 6 ÷ 60 = 144 CFM.
What are air changes per hour?
Air changes per hour, or ACH, is how many times the whole volume of air in a room is replaced in an hour. A figure of 6 means the room's air is replaced six times an hour. The right figure depends on the room and its use, so ask your designer or check local requirements.
How do you calculate CFM through a duct?
Multiply the air velocity in feet per minute by the cross-section area of the duct in square feet. An 8 inch round duct has an area of 0.349 square feet, so air moving at 600 feet per minute carries about 209 CFM.
How do I convert CFM to cubic meters per hour?
One CFM is 60 cubic feet per hour, and a cubic foot is 0.0283168 cubic meters, so 1 CFM is about 1.699 cubic meters per hour. The calculator shows both.
Can I use this to size a fan or ventilation system?
It gives the airflow for the numbers you enter. Sizing a fan also involves duct losses, fittings and code requirements, so ask a qualified HVAC contractor or designer. The result is a starting point, not a design.
For information only. Ventilation design and fan sizing need a qualified HVAC professional and must meet local code.