Extech Instruments 451112 Instruction Manual page 3

ADDENDUM: EFUL EQUATIONS AND CONVERSIONS
Area equation for rectangular or square ducts
Width (W)
Height (H)
Area (A) = Width (W) x Height (H)
Area equation for circular ducts
Cubic equations
Area (A) = T x r?
Where 7 = 3.14 and r° = radius x radius
CFM (ft3/min) = Air Velocity (ft/min) x Area (ft?)
CMM (m*/min) = Air Velocity (m/sec) x Area (m?) x 60
NOTE: Measurements made in inches
must be converted to feet or meters before using the above formulae.
Unit of Measure Conversion Table
mis ft/min knots km/h MPH
1mis 1 196.87 1.944 36 224
1 f/min 0.00508 1 0.00987 0.01829 0.01138
1 knot 0.5144 101.27 1 1.8519 1.1523
1 km/h 02778 54.69 0.54 1 0.6222
1 MPH 0.4464 87.89 0.8679 1.6071 1
4 Model 451112 Version 2.3 5/03