force per unit area is a measure of
Pressure Pressure is the amount of force applied perpendicular to the surface of an object per unit area. The symbol for it is p or P.[1] The IUPAC recommendation for pressure is a lower-case p.[2] However, upper-case P is widely used. The usage of P vs p depends upon the field in which one is working, on the nearby presence of other symbols for quantities such as power and momentum, and on writing style.