It is the pressure (P) exerted at any point by the height of the substance above that point. To convert from feet of head to pounds per square inch, the following relationship is used
P = Pressure, lbf/in2 (or psi).
γ = Specific Weight of substance
lbf/ft3 (for water = 62.3 lbf/ft3).
H= Static head, ft.
1 psi = 2.31 ft
1 bar = 10.19 m
1 m = 3.28 ft
1 bar = 14.5 psi
1 m = 9.81 KPascal