Hi, Iím trying to find the wind force acting on a flat surface. I keep coming up with two equations.

F = A x P x Cd. A = The projected area of the item. P , Wind pressure (Psf), = .00256 x V^2 (V= wind speed in Mph). Cd , Drag coefficient

And F = 1/2p*V^2*x Cd. A

In the first equation .00256 is substituted for Ĺ rho. Is this correct, and how is it derived?

I am getting 0.0023769 slugs/cu. ft. for the air mass so this doesnít make sense to me.