Model 407123 V5.2 2/2006
7
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
196.87
1.944
3.6
2.24
1 ft/min
0.00508
1
0.00987
0.01829
0.01138
1 knot
0.5144
101.27
1
1.8519
1.1523
1 km/hr
0.2778
54.69
0.54
1
0.6222
1 MPH
0.4464
87.89
0.8679
1.6071
1
A = pi x R
2
R
A = W x H
W
H
