AN310-en-GB_V1.5 11/15
12
Appendix:
Useful
Equations
and
Conversions
Area
equation
for
rectangular
or
square
ducts
Area
equation
for
circular
ducts
Cubic
equations
NOTE:
Measurements
made
in
inches
or
centimeters
must
be
converted
to
feet
or
meters
before
using
these
formulae.
Unit
of
Measure
Conversion
Table
m/s
ft/min
knots
km/h
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/h
0.2778
54.69
0.54
1
0.6222
1
MPH
0.4464
87.89
0.8679
1.6071
1
Copyright
©
2014
‐
2015
FLIR
Systems,
Inc.
All
rights
reserved
including
the
right
of
reproduction
in
whole
or
in
part
in
any
form
www.extech.com
Width
(W)
Height
(H)
Area
(A)
=
Width
(W)
x
Height
(H)
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
Radius
Area
(A)
=
pi x
r
2
Where
pi
=
3.14
and
r
2
=
radius
x
radius
