Airflow Unit Conversion
Airflow Value
LFM
m/s
MPH
CFM
m^3/hr
L/s
Velocity Units
fl/min (LFM)
m/s
miles/hr (MPH)
Velocity Units
ft3/min (CFM)
m3/hr
L/s
Choose circular or rectangular duct and type the required dimension(s), then select the appropriate units.
Rectangular
Duct
Circular Duct
Data
in
ft
mm
cm
m
Outcome
in
ft
mm
cm
m
Reset
Calculator
Airflow
Calculate
EXAMPLE
Select the appropriate DC fan to supply 400 LFM (2 m/s) airflow into a 4 inch (102 mm) diameter circular duct with a pressure drop of 0.1 inches of water (25 Pa).
Using the airflow calculator above, type the airflow value of
400
and select LFM as the units. Next type the circular duct dimensions of
r = 2 in
. After pressing the
Calculate Airflow
button, read the CFM requirement of 34.91 CFM in the volume airflow units column.
This value coupled with the pressure drop of 0.1 inches of water (25 Pa) now allows the use of standard fan curves. For example, click the following link to select a 12 volt DC fan, which meets the requirement: 12 DC Fan. Notice that the free air delivery of fans is the airflow delivered with no resistance. The fourth fan listed,
Flight II 120 - FT12B3
, would deliver 37.8 CFM into the duct and 90 CFM if no resistance was presented.