The formula for pressure is what?
In simplest terms, pressure is described as the ratio of applied force (perpendicular to an area) to the surface area over which the force is applied.
i.e, pressure = force/surface area
or, P = F/A
where, P is the pressure, F is the normal force and A is the surface area.
The units of pressure are N/m^2 (or any other area unit, such as mm^2, cm^2, etc.), Pascal, psi (pound per square inch, traditional unit), atmosphere. Pressure may also be expressed in terms of height of a particular fluid (such as water or mercury) in a manometer. There are a number of other units of pressure as well.
Just a small note, Pressure (of a liquid) can also be measured in terms of height of fluid as,
P = `rho g h`
i.e. as the product of density of fluid, acceleration due to gravity and height to which it rises.