Estimating Water Pressure at Depth

Estimating Water Pressure at Depth

(Revised May 2024)

P = (Density * G * Depth) + P_Atm

Where:

P: Pressure Exerted on Object at given Depth (Pascals or Pounds per Square Foot [psf])
Density: Fluid Density (kg/m³ or slug/ft³)
G: Acceleration of Gravity (m/sec² or ft/sec²)
Depth: Depth of Object below Fluid Surface (meters or feet)
P_Atm Atmospheric Pressure at Fluid Surface (Pascals or Pounds per Square Foot [psf])

VARIOUS NOTES RELATED TO THE EQUATION ABOVE

Atmospheric pressure at the surface is 101,325 Pascals or 2,116.22807 lb/ft²
At the surface, sea water density is about 1,025 kg/m³ or 1.988828 slug/ft³
At the surface, fresh water density is about 1,000 kg/m³ or 1.94032 slug/ft³
To convert from Pascals to Megapascals, divide by 1,000,000
To convert from pounds per square foot (psf) to pounds per square inch (psi), multiply by 0.00694444343723789.

IMPORTANT NOTE

Water is not an incompressible medium; density changes fractionally with depth. Thus, unless you have a precise chart showing density against depth, the numbers generated via this method should only be regarded as close approximations for general back of envelope calculations.

PRE-BUILT CALCULATOR

Depth

Notable Depths are:

91.5 meters / 300 ft - Gato
122 meters / 400 ft - Balao/Tench
213.5 meters / 700 ft - Type VIIC/Tang/Nautilus/Barbel
400 meters / 1,300 ft - Project 705 Lira (aka Alfa)
3,840.5 meters / 12,600 ft - RMS Titanic
4,785.4 meters / 15,700 ft - Bismarck
11,948 meters / 39,200 ft - Challenger Deep

Water Pressure (PSI)
Water Pressure (MPa)

P = (Density * G * Depth) + PAtm

PRE-BUILT CALCULATOR

P = (Density * G * Depth) + P_Atm