AN500-EU-EN v1.5 1/13
9
Useful Equations and Conversions
Area equations
The volume of air flowing through a duct or vent can be determined by taking the area of the duct
in square units (i.e. square feet) and multiplying this value by the measured linear velocity (i.e., feet
per minute). This gives: ft/min x ft
2
= ft
3
/min (CFM)
Cubic equations
CFM (ft
3
/min) = Air Velocity (ft/min) x Area (ft
2
)
CMM (m
3
/min) = Air Velocity (m/sec) x Area (m
2
) x 60
Units Conversion Table
m/s
ft/min
knots
km/hr
MPH
1 m/s
1
196.85
1.944
3.6
2.237
1 ft/min
0.00508
1
0.00987
0.01829
0.01136
1 knot
0.5144
101.27
1
1.852
1.151
1 km/hr
0.2778
54.68
0.54
1
0.6214
1 MPH
0.447
88
0.869
1.6093
1
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A = pi x R
2
R
A = W x H
W
H
