Blowing wind exerts pressure on the objects that are in its way. The amount of pressure exerted by wind on an object depends on the wind's speed and density, and the object's shape. If you know these three variables, you can easily convert wind speed to pressure in pounds per square inch (psi). Before attempting this calculation, it is useful to know that the density of dry air at sea level is roughly 1.25kg per cubic meter and that every object has a drag coefficient (C) that can be estimated based on its shape.
Write this equation converting wind speed in meters per second (m/s) to pressure in Newton per square meter (N/m^2):
Pressure = 0.5 x C x D x V^2
C = Drag coefficient D = Density of air (kg/m^3) V = Speed of air (m/s) ^ = "to the power of"
Obtain the wind speed value you wish to convert to pressure. It needs to be in meters per second or the equation will not work.
Example: V = 11m/s
Estimate the drag coefficient based on the shape of the surface of your object that faces the wind.
Example: C for one face of a cubic object = 1.05
Sphere: 0.47 Half-Sphere: 0.42 Cone = 0.5 Corner of a Cube = 0.8 Long Cylinder = 0.82 Short Cylinder = 1.15 Streamlined body = 0.04 Streamlined half-body = 0.09
For additional information regarding these shapes, visit the link in the Resources section.
Plug the values into the equation and calculate your answer:
Pressure = 0.5 x 1.05 x 1.25kg/m^3 x (11m/s)^2 = 79.4 N/m^2
Perform any necessary conversions to the units you desire. The wind speed must be in meters per second for the equation to be accurate.
Convert mph to meters per second (m/s) by multiplying the speed in mph by 0.447. This value is obtained by dividing the number of meters in 1 mile, 1609, by the number of seconds in 1 hour, 3600.
Example: 23mph x 0.447 = 10.3m/s
Convert Newton per square meter (N/m^2) to psi by multiplying the pressure in N/m^2 by 0.000145. This number is based on the number of Newtons in a pound and the number of square inches in a square meter.
Example: 79.4 N/m^2 x 0.000145 = 0.012 psi
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