Extech Instruments 407119A User Manual page 9

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
1 m/s
1 ft/min
1 knot
1 km/h
1 MPH
Height (H)
Area (A) = Width (W) x Height (H)
Where pi= 3.14 and r
3
/min) = Air Velocity (ft/min) x Area (ft
3
/min) = Air Velocity (m/sec) x Area (m
NOTE: Measurements made in inches
m/s ft/min
1 196.87
0.00508 1
0.5144 101.27
0.2778 54.69
0.4464 87.89
Area (A) = pi x r 2
2
= radius x radius
knots km/h
1.944 3.6
0.00987 0.01829
1 1.8519
0.54
0.8679 1.6071
9
2
)
2
) x 60
MPH
2.24
0.01138
1.1523
1 0.6222
1
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