Hydrostatic Pressure at Depth Calculator
Hydrostatic pressure is the pressure created by a column of fluid at rest, and it rises in direct proportion to depth. Divers, civil engineers, tank designers, and aquarium builders all rely on this relationship to size structures and predict loads. The pressure depends only on fluid density, gravitational acceleration, and the vertical depth below the surface, not on the shape of the container. Enter the fluid density, local gravity, the depth, and the pressure acting on the surface; this calculator returns the gauge pressure, the absolute pressure, and the equivalent values in kilopascals and atmospheres.
Hydrostatic pressure formula
Gauge pressure = rho * g * h
Absolute pressure = surface pressure + gauge pressure
1 kilopascal = 1,000 pascals
1 atmosphere = 101,325 pascals
rho is fluid density in kilograms per cubic metre, g is gravitational acceleration in metres per second squared, and h is depth in metres. The result is in pascals. Absolute pressure adds the pressure acting on the fluid surface.
Fluid pressure context
- Pressure depends only on depth and density, not on the volume or shape of the fluid body (the hydrostatic paradox).
- Standard atmospheric pressure at sea level is 101,325 pascals (one standard atmosphere) per the BIPM definition.
- Fresh water density is near 1,000 kg/m^3; seawater is about 1,025 kg/m^3; mercury is about 13,534 kg/m^3.
- Standard gravity is 9.80665 m/s^2; use a local value for high-precision work.
- Set surface pressure to zero to obtain gauge pressure only, or to 101,325 for an open body of water at sea level.
Pressure at depth: frequently asked questions
What is hydrostatic pressure?
Hydrostatic pressure is the pressure exerted by a fluid at rest due to the weight of fluid above a point. It increases linearly with depth and is given by P = rho x g x h, where rho is fluid density, g is gravitational acceleration, and h is depth below the free surface.
What is the difference between gauge and absolute pressure?
Gauge pressure is the hydrostatic pressure of the fluid column alone, rho x g x h. Absolute pressure adds the pressure pushing on the fluid surface, usually atmospheric pressure. This calculator reports gauge pressure and absolute pressure using the surface pressure you enter.
What density should I use for water?
Fresh water is approximately 997 kg/m^3 at 25 degrees Celsius and 1,000 kg/m^3 at 4 degrees Celsius. Standard seawater is about 1,025 kg/m^3. Density is a user-editable input so you can match your specific fluid and temperature.
What value of gravity should I use?
Standard gravity is defined as 9.80665 metres per second squared by the BIPM. Local gravity varies slightly with latitude and altitude, from about 9.78 at the equator to 9.83 near the poles. The field is editable so you can enter a local value.
How much does pressure rise per metre of water?
In fresh water of density 1,000 kg/m^3 under standard gravity, pressure rises by about 9,807 pascals (9.807 kilopascals) per metre of depth, roughly one tenth of an atmosphere. In seawater the rise is slightly larger because the density is higher.
Official sources
- BIPM: SI units, the pascal and standard gravity.
- NIST Physical Measurement Laboratory: Units and conversion factors (SP 811).
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.