Fluid Pressure Calculator
The pressure inside a still fluid grows with depth because of the weight of the fluid above. This hydrostatic relationship, pressure equals density times gravity times depth, underlies everything from dam design to scuba diving limits. This calculator takes the fluid density, the depth, and the gravitational acceleration and returns the gauge pressure in pascals, kilopascals, and atmospheres. Density and gravity are editable so you can model fresh water, seawater, other liquids, or even other planets, and the result reflects exactly the fluid you describe.
Fluid pressure formula
P = rho * g * h (pascals, gauge)
rho = density (kg/m^3), g = gravity (m/s^2), h = depth (m)
kilopascals = P / 1,000
atmospheres = P / 101,325
absolute pressure = P + 101,325 pascals (sea-level atmosphere)
One standard atmosphere is defined as exactly 101,325 pascals. Standard gravity is 9.80665 metres per second squared. The gauge formula excludes atmospheric pressure; the absolute figure adds it back.
Fluid pressure facts
- Fresh water is about 1,000 kilograms per cubic metre; seawater about 1,025.
- Pressure rises by roughly one atmosphere for every 10 metres of seawater depth.
- Hydrostatic pressure depends only on depth, not on the container's shape or width.
- One pascal is one newton per square metre, the SI unit of pressure.
- Standard atmospheric pressure at sea level is 101,325 pascals.
Fluid pressure: frequently asked questions
What is hydrostatic pressure?
Hydrostatic pressure is the pressure a fluid at rest exerts because of gravity acting on the fluid above a point. It increases with depth and equals fluid density times gravitational acceleration times depth (P = rho * g * h). It does not depend on the container's shape, only on the depth below the surface.
What is the formula for fluid pressure?
The gauge (hydrostatic) pressure is P = rho * g * h, where rho is the fluid density in kilograms per cubic metre, g is gravitational acceleration in metres per second squared, and h is the depth in metres. The result is in pascals. This is the pressure due to the fluid column above the depth, excluding atmospheric pressure.
What density should I enter?
Use the density of your fluid. Fresh water is about 1,000 kilograms per cubic metre, seawater roughly 1,025, and other liquids differ. Because density depends on the fluid, temperature, and salinity, it is a user-editable input here rather than a fixed assumption.
Does this include atmospheric pressure?
No. The formula gives gauge pressure, the pressure from the fluid column alone. To get absolute pressure, add the atmospheric pressure at the surface, about 101,325 pascals at sea level. Many engineering problems use gauge pressure directly because instruments often read relative to atmosphere.
Why is gravity an input?
Standard gravity is 9.80665 metres per second squared, the value set by international convention, and it is the default here. Local gravity varies slightly with latitude and altitude, and other planets differ entirely, so the field is editable for those who need a different value.
Official sources
- National Institute of Standards and Technology (NIST): SI units, the pascal.
- National Institute of Standards and Technology (NIST): Standard acceleration of gravity.
Reviewed by the CalculatorHub team, edited by James Graham, 16 June 2026. See our methodology.