Hydrostatic pressure
Pressure at a depth (P = P₀ + ρgh) or depth of a gauge pressure, both gauge and absolute, with the usual fluids.
Result
201 840 Pa
- Calculation
- ΔP = ρ·g·h = 1025 kg/m³ × 9.80665 × 10 m = 100 520 Pa
- Absolute pressure
- 2.0184 bar, that is 1.992 atm
- Gauge pressure (relative)
- 100 520 Pa
- Absolute pressure
- 201 840 Pa
- One more atmosphere every
- 10.08 m
Notes (2)
The column adds 100 520 Pa of gauge pressure: the absolute pressure is 2.0184 bar, that is 1.992 atm.
Diver’s rule "one bar every ten metres": exact value 9.95 m per bar in sea water, 10.2 m in fresh water.
Calculation, assumptions and sources
OverviewPressure h metres below the surface of a fluid, or depth of a given gauge pressure.
Pressure h metres below the surface of a fluid, or depth of a given gauge pressure. Gauge pressure (read on the manometer) and absolute pressure are given together, in pascals, bars and atmospheres. Usual fluids preset, adjustable surface pressure (0 for a vacuum tank).
Method & formulasΔP = ρ × g × h
The gauge pressure ρ·g·h is the weight of the fluid column per unit area; it adds to the surface pressure. The inverse calculation gives the column height equivalent to a pressure: one atmosphere is 760 mm of mercury or 10.3 m of water.
- Gauge pressure
- the pressure counted from the surface, zero at the surface. Usual manometers (diving, tyres) read it.
- Absolute pressure
- the pressure counted from vacuum, one atmosphere at the surface. The ideal gas law and physiology use it.
- Standard atmosphere
- exactly 101,325 Pa, by definition. Equals 1.01325 bar.
- Column height
- the depth of fluid that produces a given pressure: the unit of barometers (mmHg) and head losses (metres of water column).
Validity domainIncompressible fluid at rest: valid for liquids at usual depths (water compresses by 0.5% per kilometre).
Incompressible fluid at rest: valid for liquids at usual depths (water compresses by 0.5% per kilometre). In the atmosphere, over large heights, the air density decreases and the pressure follows an exponential. g is uniform, at its conventional standard value 9.80665 m/s².
Reading the resultIn diving, absolute pressure governs nitrogen dissolution: at 30 m, the breathed air is at 4 atm and nitrogen dissolves four times more, hence decompression stops.
In diving, absolute pressure governs nitrogen dissolution: at 30 m, the breathed air is at 4 atm and nitrogen dissolves four times more, hence decompression stops. The shape of the container plays no role; only the vertical height counts (hydrostatic paradox).