Write down the generic wind load equation, which states that wind force (F) is equal to the projected area of impact (A) multiplied by the wind pressure in pounds per square foot (P) multiplied by the drag coefficient (Cd). Expressed in an equation, F = A * P * Cd.
Calculate the projected area of impact. For simple rectangular surfaces, this is the object's width multiplied by its height. For example, a wall that measures 20 feet by 10 feet has an area of 200 square feet.
Calculate the wind pressure in pounds per square foot. Wind pressure is equal to the wind velocity squared, in miles per hour, multiplied by .00256 (P = V^2 * .00256). A 30 mph wind has a wind pressure of 2.304 pounds per square foot (P = 30^2 * .00256 = 2.304 psf).
Write down the drag coefficient of the surface. For flat surfaces, this is 2.0, and for long cylinders it is equal to 1.2. The wall in the example is flat, thus the drag coefficient is 2.0.
Substitute the area, wind pressure and drag coefficient into the equation (F = 200 * 2.304 * 2.0).
Solve the equation to calculate the wind force on the structure's surface. In the example, F = 200 * 2.304 * 2.0 = 921.6 pounds.