The piezometric tube or piezometer is a tube in which, being connected on one side to a container in which a fluid is located, the level rises to a height equivalent to the pressure of the fluid at the connection point or piezometric orifice, that is, up to its loading level. Said height H is the sum of the pressure head h and the elevation z. In a piezometric tube, the pressure is the same as that inside the reservoir containing the fluid.

The pressure can be expressed, according to the hydrostatic equation, as:.

Where:.

These piezometric tubes are also frequently used to determine the static component of pressure in pipes.