Hydrostatic Pressure Calculator

What is hydrostatic pressure?

Hydrostatic pressure is the pressure at a point in a liquid at rest caused by the weight of the liquid column above it. The relation is short: p = ρ × g × h, where ρ is the liquid density, g the acceleration of gravity and h the vertical depth below the surface. The pressure does not depend on the shape or width of the vessel, only on depth.

Gauge and absolute pressure

The formula gives gauge pressure, which is what a pressure gauge reads. Adding the pressure at the surface gives absolute pressure: p_abs = p0 + ρ × g × h. For an open tank p0 is atmospheric pressure.

Example

Water 10 metres deep has a gauge pressure of 1000 × 9.80665 × 10 = 98 066 Pa, or 0.98 bar. As a rule of thumb every 10 metres of water adds about 1 bar. At sea level the absolute pressure comes to 0.98 + 1.01 = 1.99 bar. Going the other way, a gauge reading 2.5 bar corresponds to a water height of 25.5 metres.

Limits

The calculation is for a liquid that is at rest and incompressible. In a flowing liquid, velocity and friction losses come into play as well. Density changes with temperature, so enter the correct density manually for hot water or brine. Forces on tank walls and strength checks are outside this calculator.