CFM Converter
Convert airflow between cubic feet per minute (CFM), liters per second (L/s), and cubic meters per hour (m3/h).
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Airflow is measured in different units depending on region.
Conversion factors:
- 1 CFM = 0.4720 L/s (liters per second)
- 1 CFM = 1.6990 m3/h (cubic meters per hour)
- 1 L/s = 2.1189 CFM = 3.6 m3/h
- 1 m3/h = 0.5886 CFM = 0.2778 L/s
Common HVAC airflow values:
- Bathroom fan: 50-110 CFM (24-52 L/s)
- Kitchen range hood: 100-400 CFM (47-189 L/s)
- Central AC (per ton): 400 CFM (189 L/s)
- Whole house fan: 3,000-6,000 CFM (1,416-2,832 L/s)
Ventilation standards:
- ASHRAE recommends 15-20 CFM per person for office spaces.
- Residential: about 0.35 air changes per hour.
CFM is really a way of asking how fast the air in a space gets replaced. To size a fan, take the room’s volume in cubic feet, multiply by the air changes per hour you want, and divide by 60. A 1,000 cubic-foot bathroom that needs 8 air changes an hour wants about 133 CFM, so a 110 CFM fan would be a touch undersized.
The catch is that a fan’s rated CFM is measured on a test bench with no resistance. Add real ducting, elbows, and a roof cap and the actual airflow can drop well below the box number, sometimes by half on a long, twisty run. That’s why experienced installers size up and keep duct runs short and straight rather than trusting the rated figure at face value.
How we build and check this converter
This converter runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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