A vertical column of fluid exerts a pressure due to the column’s weight. The relationship between column height and fluid pressure at the bottom of the column is constant for any particular fluid (density) regardless of vessel width or shape.

This principle makes it possible to infer the height of liquid in a vessel by measuring the pressure generated at the bottom:


The mathematical relationship between liquid column height and pressure is as follows:
P = ρgh      P = γh
P = Hydrostatic pressure
ρ = Mass density of fluid in kilograms per cubic meter (metric) or slugs per cubic foot (British)
g = Acceleration of gravity
γ =Weight density of fluid in newtons per cubic meter (metric) or pounds per cubic foot (British)
h = Height of vertical fluid column above point of pressure measurement

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