Pressure is the amount of force acting per unit area. The symbol of pressure is p or P.
Pressure is expressed in various units. Some of these derive from a unit of force divided by a unit of area. The SI unit of pressure, the pascal (Pa), for example, is one newton per square meter. Similarly, the pound-force per square inch (psi) is the traditional unit of pressure in the imperial and US customary systems.
Pressure may also be expressed in terms of standard atmospheric pressure; the atmosphere (atm) is equal to this pressure and the torr is defined as 1⁄760 of this.