Extech Instruments 407119A User Manual page 11

Useful Equations and Conversions
Area equation for rectangular or square ducts
Width (W)
Area equation for circular ducts
Radius
Cubic equations
CFM (ft
CMM (m
must be converted to feet or meters before using the above formulae.
Unit of Measure Conversion Table
m/s
1 m/s 1
1 ft/min 0.00508
1 knot 0.5144
1 km/h 0.2778
1 MPH 0.4464
Height (H)
Area (A) = Width (W) x Height (H)
Area (A) =
Where
3
/min) = Air Velocity (ft/min) x Area (ft
3
/min) = Air Velocity (m/sec) x Area (m
NOTE: Measurements made in inches
ft/min
196.87
1
101.27
54.69
87.89
11
2
x r
= 3.14 and r 2 = radius x radius
knots km/h
1.944 3.6
0.00987 0.01829
1 1.8519
0.54 1
0.8679 1.6071
Model 407119A Version 5.0 October 2005
2
)
2
) x 60
MPH
2.24
0.01138
1.1523
0.6222
1