Useful Conversions

You can find many useful conversions that are used in ventilation below

Units Multiplied By Units Units Multiplied By Units
Length
Millimeters 0.1 Centimeters Centimeters 10 Millimeters
Inches 2.54 Centimeters Centimeters 0.3937 Inches
Feet 0.3048 Meters Meters 3.2808 Feet
Yards 0.9144 Meters Meters 1.0936 Yards
Area 
Square Inches 6.4516 Square Centimeters Square Centimeters 0.1550 Square Inches
Square Feet 0.0929 Square Meters Square Meters 10.7640 Square Feet
Volume
Cubic Feet 0.0283 Cubic Meters Cubic Meters 35.3144 Cubic Feet
Cubic Yards 0.7646 Cubic Meters Cubic Meters 1.3079 Cubic Yards
Gallons 4.5461 Litres Litres 0.2130 Gallons
Weight
Foot-Pounds 1.3830 Newton-Meters Newton-Meters 0.7380 Foot-Pounds
Pounds 0.4536 Kilograms Kilograms 2.2046 Pounds
Volume Flow Rate
1 m3/s = 999.97 l/s = 3600 m3/h = 2118.9 cfm = 60 m3/min
1 l/s = 3.60 m3/h = 2.119 cfm = 0.06m3/min = 0.001 m3/s
1 m3/h = 0.5886 cfm = 0.01667 m3/min = 0.00028 m3/s = 0.2778 l/s
1 cfm = 0.0283 m3/min = 0.000472 m3/s = 0.4719 l/s = 1.699 m3h
1 m3/min = 0.01667 m3/s = 16.67 l/s = 60 m3/h = 35.315 cfm
Velocity
1 m/s = 196.85 ft/min
1 ft/min = 0.00508 m/s
Pressure
1 Pa = 0.01 mbar = 0.004015 in.wg = 0.10197 mm.wg = 0.000145 psi
1 mbar = 0.4015 in.wg = 10.197 mm.wg = 0.0145 psi = 100 Pa
1 in.wg = 25.4 mm.wg = 0.0361 psi = 249.089 Pa = 2.49089 mbar
1 mm.wg = 0.00142 psi = 9.80665 Pa = 0.09807 mbar = 0.03937 in.wg
1 psi = 6894.76 Pa = 68.9476 mbar = 27.68 in.wg = 703.07 mm.wg

It is recommended that the following multiples and sub-multiples of the S.I. units are used in fan technology:

Pressure kilopascal = kPa = 1000 Pa
Barometric Pressure millibar = mbar = 100 Pa
Volume Flow Rate Litre per second = l/s = 10-3m3/s

Converting dB to dB(A)

Different manufacturers provide different sound levels at different distances. The following graph enables you to get an equal sound reading by showing you the changes in sound at different distances:

Example: A fan has a dB(A) level of 40 at 1m and you want to know the value at 3m. Follow the horizontal axis across to 3 and go down until you hit the diagonal line, which brings you to -21. Then do the same for 1m in distance. This will give you a value of -11.

-11 subtracted from -21 = -10

Subtract -10 from the 1m value (40) = 30 dB(A) at 3m from the fan.

If you have the dB value then use this graph to find the dB(A) at the relevant distance you require.