Calculating Pressure on anObject immersed in a Fluid

The Precise Way

Pressure = (DensityFluid * GravityAcceleration * DepthObject) + PressureAtmosphere

Whereas:

Pressure: Pressure exterted on the object. Measured in either Pascals or PSI.
DensityFluid: Density of the fluid the object is immersed in. Measured in either kg/m3 or slugs/ft3.

Freshwater is about 1,000 kg/m3 (1.94 slug/ft3)
Seawater is about 1,030 kg/m3 (1.99 slug/ft3)

GravityAcceleration: Acceleration of Gravity. On Earth, it's either 9.8 m/sec2 or 32 ft/sec2 .
DepthObject: Depth of the object below the fluid's surface. Measured in either meters or feet.
PressureAtmosphere: Atmospheric pressure at sea level. On Earth, this is either 101,325 Pascals or 14.696 PSI.

EXAMPLE: A submarine is at a depth of 200 meters in seawater. What is the pressure on the hull of the submarine?

(1030 kg/m3 * 9.8 m/sec2 * 200) + 101,325 Pascals = 2,120,125 Pascals (or 2.12 megapascals)

NOTES:

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.

Megapascals to PSI conversion factor: 145 (2.12 megapascals would be about 307.4 PSI.)

The Simple Way

Metric

MPa (Freshwater) = 0.1013 + (0.009 * DepthMeters)
MPa (Saltwater) = 0.1013 + (0.01 * DepthMeters)

US Customary

PSI (Freshwater) = 14.968 + (0.433 * DepthFeet)
PSI (Saltwater) = 14.976 + (0.446 * DepthFeet)

CHEAT SHEET

 Fresh Water(1000 kg/m3) Sea Water(1030 kg/m3) Depth(meters/feet) Pressure(MPa/PSI) Pressure(MPa/PSI) 15.25 meters(50 feet) 0.3 MPa36.4 PSI 0.3 MPa37 PSI 30.48 meters(100 feet) 0.4 MPa58 PSI 0.4 MPa59.3 PSI 61 meters(200 feet) 0.7 MPa101.4 PSI 0.7 MPa104 PSI 91.5 meters(300 feet)Gato 1 MPa144.8 PSI 1 MPa148.7 PSI 122 meters(400 feet)Balao/Tench 1.3 MPa188.1 PSI 1.3 MPa193.3 PSI 152.5 meters(500 feet) 1.6 MPa231.5 PSI 1.6 MPa238 PSI 183 meters(600 feet) 1.9 MPa274.8 PSI 1.9 MPa282.6 PSI 213.5 meters(700 feet)Tang/Nautilus/Barbel 2.2 MPa318.2 PSI 2.3 MPa327.3 PSI 244 meters(800 feet) 2.5 MPa361.5 PSI 2.6 MPa371.9 PSI 274.5 meters(900 feet) 2.8 MPa404.9 PSI 2.9 MPa416.6 PSI 305 meters(1,000 feet) 3.1 MPa448.2 PSI 3.2 MPa461.2 PSI 366 meters(1,200 feet) 3.7 MPa534.9 PSI 3.8 MPa550.5 PSI 427 meters(1,400 feet) 4.3 MPa621.6 PSI 4.4 MPa639.8 PSI 488 meters(1,600 feet) 4.9 MPa708.3 PSI 5 MPa729.1 PSI 549 meters(1,800 feet) 5.5 MPa795 PSI 5.6 MPa818.4 PSI 610 meters(2,000 feet) 6.1 MPa881.7 PSI 6.3 MPa907.7 PSI 914.4 meters(3,000 feet) 9.1 MPa1,314.4 PSI 9.3 MPa1,353.4 PSI 1,219.2 meters(4,000 feet) 12 MPa1,747.6 PSI 12.4 MPa1,799.6 PSI 1,525 meters(5,000 feet) 15MPa2,182.3 PSI 15.5 MPa2,247.3 PSI 3,048 meters(10,000 feet) 30 MPa4,347 PSI 30.9 MPa4,477 PSI 3,840.5 meters(12,600 feet)RMS Titanic 37.7 MPa5,473.5 PSI 38.9 MPa5,637.2 PSI 4,785.4 meters (15,700 feet)Bismarck 47 MPa6,816.5 PSI 48.4 MPa7,020.6 PSI 11,948 meters(39,200 feet)Challenger DeepMarianas Trench 117.2 MPa16,997.2 PSI 120.7 MPa17,506.7 PSI