Useful Equations and Conversions
Area equation for rectangular or square ducts
Height (H)
Area (A) = Width (W) x Height (H)
Width (W)
Area equation for circular ducts
Radius
Area (A) =
Where
x r
2
= 3.14 and r
2
= radius x radius
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
NOTE:
Measurements made in
inches
must be converted to
feet
or
meters
before using the above formulae.
Unit of Measure Conversion Table
m/s
1 m/s
1 ft/min
1 knot
1 km/h
1 MPH
1
0.00508
0.5144
0.2778
0.4464
ft/min
196.87
1
101.27
54.69
87.89
knots
1.944
0.00987
1
0.54
0.8679
km/h
3.6
0.01829
1.8519
1
1.6071
MPH
2.24
0.01138
1.1523
0.6222
1
8
Model 407114 Version 2.0 November 2005
EXTECH [ EXTECH INSTRUMENTS CORPORATION. ]
