Calculate water pressure from depth or head height in psi, kPa or bar, convert pressure back to feet of head, or adjust for a fixture’s elevation.
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Water Pressure Formula
For a static, constant-density fluid, the pressure increase below an upper reference is density times gravity times vertical head. Absolute pressure at depth also includes the upper reference pressure.
- Where ΔP is the pressure increase below the reference, in Pa
- ρ is the assumed constant fluid density, in kg/m³
- g is gravitational acceleration magnitude, in m/s²
- h is vertical liquid head below the reference, in m
Use ΔP = ρgh for pressure increase and h = ΔP/(ρg) for equivalent head. If the upper surface is atmospheric, the increase is gauge pressure. For absolute pressure use Pabsolute = Preference,absolute + ΔP. For a fixture above a source, Pfixture,gauge = Psource,gauge − ρgΔz; below the source, add the elevation contribution. A signed negative gauge result is a formal sub-atmospheric prediction, not proof of a stable filled column or delivery at an open fixture. Air entry, venting, vapor pressure, flow friction and pump performance are not modeled. See OpenStax hydrostatics and gauge and absolute pressure.
The freshwater preset assumes 998 kg/m³ and the seawater preset assumes 1,025 kg/m³. These are approximate examples; density depends on temperature, salinity and pressure. Supply the relevant density when known.
Standard gravity is 9.80665 m/s²; actual local gravity varies. The optional gravity field is editable and must be positive. Length, pressure and supplied-density units convert existing quantities when changed.
Water Pressure Definition
Hydrostatic pressure varies with vertical elevation in a static fluid. The calculator reports pressure differences or gauge-pressure scenarios; it does not automatically include atmospheric pressure or predict residual pressure during flow.
Water Pressure Example
How to calculate water pressure?
- First, determine the density of the water.
Choose an explicit density assumption or supply density for the relevant water conditions.
- Next, determine the depth of the object.
Determine the total depth the object is submerged at.
- Finally, calculate the water pressure.
Use the equation for pressure increase and identify the reference. For example, 10 m at 998 kg/m³ and 9.80665 m/s² gives 97.870367 kPa pressure increase.
FAQ
A static liquid develops a pressure increase with depth of ρgh under the constant-density model. The absolute pressure at depth includes the pressure at the reference surface; gauge pressure is relative to atmosphere.
At equal vertical head and gravity, the denser liquid has the larger hydrostatic pressure increase. Freshwater and seawater densities vary with temperature, salinity and pressure; the calculator presets are illustrative assumptions.
The default is standard gravity, 9.80665 m/s². Actual gravity varies with location and elevation, and differs on other bodies. Supply a positive acceleration magnitude for the scenario.
