In fluid mechanics, pressure head is the height of a liquid column that corresponds to a particular pressure exerted by the liquid column on the base of its container. It may also be called static pressure head or simply static head (but not static head pressure).

Mathematically this is expressed as:

${\displaystyle \psi ={\frac {p}{\gamma }}={\frac {p}{\rho \,g}}}$

where

${\displaystyle \psi }$ is pressure head (which is actually a length, typically in units of meters or centimetres of water)

${\displaystyle p}$ is fluid pressure (i.e. force per unit area, typically expressed in pascals)

${\displaystyle \gamma }$ is the specific weight (i.e. force per unit volume, typically expressed in N/m³ units)

${\displaystyle \rho }$ is the density of the fluid (i.e. mass per unit volume, typically expressed in kg/m³)

${\displaystyle g}$ is acceleration due to gravity (i.e. rate of change of velocity, expressed in m/s²).

Note that in this equation, the pressure term may be gauge pressure or absolute pressure, depending on the design of the container and whether it is open to the ambient air or sealed without air.