How can you calculate the stalling speed of an average airplane?

[dalyningkenk]

The stalling speed is the speed that is equal to the drag or air resistance to the plane. Once the plane can overcome the drag, it can lift off.
Please help, a formula or something would be nice.

[Hawke]

Drag is a force, so it cannot be equal to a speed.

In unaccelerated flight, weight (W) = lift (L).

W = L = C(L) * 0.5 * rho * V^2 * S
where C(L) is the coefficient of lift,
rho = density
S = surface area
V = airspeed

In order to find the stall speed, you need to know the C(L) at which the wing stalls.  Once you determine that C(L):

Rearrange the equation to:
V(stall) = sqrt(2*W/(C(L)*rho*S))