Calculating Pressure on an
Object 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 MPa
36.4 PSI

0.3 MPa
37 PSI

30.48 meters
(100 feet)

0.4 MPa
58 PSI

0.4 MPa
59.3 PSI

61 meters
(200 feet)

0.7 MPa
101.4 PSI

0.7 MPa
104 PSI

91.5 meters
(300 feet)
Gato

1 MPa
144.8 PSI

1 MPa
148.7 PSI

122 meters
(400 feet)
Balao/Tench

1.3 MPa
188.1 PSI

1.3 MPa
193.3 PSI

152.5 meters
(500 feet)

1.6 MPa
231.5 PSI

1.6 MPa
238 PSI

183 meters
(600 feet)

1.9 MPa
274.8 PSI

1.9 MPa
282.6 PSI

213.5 meters
(700 feet)
Tang/Nautilus/Barbel

2.2 MPa
318.2 PSI

2.3 MPa
327.3 PSI

244 meters
(800 feet)

2.5 MPa
361.5 PSI

2.6 MPa
371.9 PSI

274.5 meters
(900 feet)

2.8 MPa
404.9 PSI

2.9 MPa
416.6 PSI

305 meters
(1,000 feet)

3.1 MPa
448.2 PSI

3.2 MPa
461.2 PSI

366 meters
(1,200 feet)

3.7 MPa
534.9 PSI

3.8 MPa
550.5 PSI

427 meters
(1,400 feet)

4.3 MPa
621.6 PSI

4.4 MPa
639.8 PSI

488 meters
(1,600 feet)

4.9 MPa
708.3 PSI

5 MPa
729.1 PSI

549 meters
(1,800 feet)

5.5 MPa
795 PSI

5.6 MPa
818.4 PSI

610 meters
(2,000 feet)

6.1 MPa
881.7 PSI

6.3 MPa
907.7 PSI

914.4 meters
(3,000 feet)

9.1 MPa
1,314.4 PSI

9.3 MPa
1,353.4 PSI

1,219.2 meters
(4,000 feet)

12 MPa
1,747.6 PSI

12.4 MPa
1,799.6 PSI

1,525 meters
(5,000 feet)

15MPa
2,182.3 PSI

15.5 MPa
2,247.3 PSI

3,048 meters
(10,000 feet)

30 MPa
4,347 PSI

30.9 MPa
4,477 PSI

3,840.5 meters
(12,600 feet)
RMS Titanic

37.7 MPa
5,473.5 PSI

38.9 MPa
5,637.2 PSI

4,785.4 meters
(15,700 feet)
Bismarck

47 MPa
6,816.5 PSI

48.4 MPa
7,020.6 PSI

11,948 meters
(39,200 feet)
Challenger Deep
Marianas Trench

117.2 MPa
16,997.2 PSI

120.7 MPa
17,506.7 PSI