Pressure at Depth

This calculator's P = ρgh formula computes GAUGE pressure -- the pressure added by the fluid column alone, measured relative to the surrounding atmosphere. It does not include the air pressure already pushing down on the fluid's surface. To get absolute pressure (what a diver's gauge or a submerged sensor actually reads), add standard atmospheric pressure at sea level, 101,325 Pa, to the hydrostatic pressure this calculator returns.

At seawater's typical density of 1,025 kg/m³, 10 meters of depth adds roughly 100,500 Pa (about 1 bar, or roughly 14.6 psi) of gauge pressure -- close to the familiar diving rule of thumb that pressure increases by about one atmosphere for every 10 meters (33 feet) of seawater. Fresh water, being slightly less dense at 1,000 kg/m³, adds a touch less pressure per meter of depth.

Yes -- because pressure is directly proportional to density in the P = ρgh formula, mercury (about 13,600 kg/m³) produces roughly 13.6 times more pressure than fresh water at the exact same depth. A barometric mercury column only needs to be about 76 cm tall to balance one atmosphere of pressure, versus over 10 meters of water to do the same job.

It usually doesn't matter "more" in the formula -- both depth and density scale pressure identically and neither dominates the other mathematically. What changes in practice is the achievable RANGE: engineers can pick a working fluid, but depth is often set by the application (a dive profile, a tank height, a pipeline route), so depth swings over a much wider practical range and tends to drive the largest pressure changes in a given project.