Subsea calculator
Depth to pressure calculator
Convert an operating depth into the pressure a housing, penetrator or foam block actually has to hold back — in bar, psi, MPa and atmospheres, for seawater or fresh water.
Estimation tool, not design authority. This calculator gives a first-pass figure from the stated method and the assumptions listed below the result. It does not replace engineering sign-off, and it does not model everything a real build has to account for — see “Assumptions and limits” for what is left out. For a figure you can build against, send us the requirement.
Result
Why it matters
Depth ratings are pressure ratings.
A component rated to 300 m is really rated to the pressure 300 m of water exerts. Working in the pressure the part will see, rather than the depth number on the label, is what lets you compare an acrylic tube quoted in metres against a foam grade quoted in MPa and a test chamber quoted in bar.
The rule of thumb is one bar per ten metres, which is close enough for conversation and about 0.5% optimistic in seawater. For specification work, use the calculated figure: at 1,000 m the difference between the rule of thumb and reality is over five bar.
How it is calculated
Hydrostatic pressure.
Gauge pressure is the weight of the water column above a point: p = ρ × g × h, with ρ the water density, g standard gravity at 9.80665 m/s² and h the depth. Absolute pressure adds one atmosphere on top, which is what an absolute sensor reads and what matters if you are calculating a pressure differential across a housing wall.
Seawater is taken at 1025 kg/m³ and fresh water at 1000 kg/m³. Real seawater density varies with temperature, salinity and — very slightly — depth itself; for design margin, work to the higher density rather than the average.
Related
Other calculators and guides.
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