In fluid mechanics, the Tait equation is an equation of state, used to relate liquid density to hydrostatic pressure. The equation was originally published by Peter Guthrie Tait in 1888 in the form where is the hydrostatic pressure in addition to the atmospheric one, is the volume at atmospheric pressure, is the volume under additional pressure , and are experimentally determined parameters.A very detailed historical study on the Tait equation with the physical interpretation of the two parameters and is given in reference.