Pressure is defined as a measure of the force applied over a unit area. Pressure often is expressed in units of Pascals (Pa), newtons per square meter (N/m2 or kg/m.s2), or pounds per square inch. Other units include the atmosphere (atm), torr, bar, and meters sea water (msw).

In equations, pressure is denoted by the capital letter P or the lowercase letter p.

Pressure is a derived unit, generally expressed according to the units of the equation:

P = F / A

where P is pressure, F is force, and A is area

P is pressure

F is the component of force perpendicular to the surface

A is the area of the surface

When a force is constant over an area, the pressure acting on that area is simply

Pressure is a scalar quantity, thus it acts in all directions at any given point. In order for pressure to create a force, the pressure must be integrated over some area.