Calculating
Pressure on an 
The Precise Way
Pressure = (Density_{Fluid} * Gravity_{Acceleration} * Depth_{Object}) + Pressure_{Atmosphere}
Whereas:
Pressure: Pressure
exterted on the object. Measured in either Pascals or
PSI.
Density_{Fluid:
}Density of the fluid the object is immersed in.
Measured in either kg/m^{3} or slugs/ft^{3}.
Freshwater
is about 1,000 kg/m^{3} (1.94 slug/ft^{3})
Seawater
is about 1,030 kg/m^{3} (1.99 slug/ft^{3})
Gravity_{Acceleration}:
Acceleration of Gravity. On Earth, it's either 9.8 m/sec^{2}
or 32 ft/sec^{2 }.
Depth_{Object}:
Depth of the object below the fluid's surface. Measured in either
meters or feet.
Pressure_{Atmosphere:}
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/m^{3} * 9.8 m/sec^{2} * 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 * Depth_{Meters})
MPa
(Saltwater) = 0.1013 + (0.01 * Depth_{Meters})
US Customary
PSI
(Freshwater) = 14.968 + (0.433 * Depth_{Feet})
PSI
(Saltwater) = 14.976 + (0.446 * Depth_{Feet})
CHEAT SHEET

Fresh Water 
Sea Water 
Depth 
Pressure 
Pressure 
15.25 meters 
0.3 MPa 
0.3 MPa 
30.48 meters 
0.4 MPa 
0.4 MPa 
61 meters 
0.7 MPa 
0.7 MPa 
91.5 meters 
1 MPa 
1 MPa 
122 meters 
1.3 MPa 
1.3 MPa 
152.5 meters 
1.6 MPa 
1.6 MPa 
183 meters 
1.9 MPa 
1.9 MPa 
213.5 meters 
2.2 MPa 
2.3 MPa 
244 meters 
2.5 MPa 
2.6 MPa 
274.5 meters 
2.8 MPa 
2.9 MPa 
305 meters 
3.1 MPa 
3.2 MPa 
366 meters 
3.7 MPa 
3.8 MPa 
427 meters 
4.3 MPa 
4.4 MPa 
488 meters 
4.9 MPa 
5 MPa 
549 meters 
5.5 MPa 
5.6 MPa 
610 meters 
6.1 MPa 
6.3 MPa 
914.4 meters 
9.1 MPa 
9.3 MPa 
1,219.2 meters 
12 MPa 
12.4 MPa 
1,525 meters 
15MPa 
15.5 MPa 
3,048 meters 
30 MPa 
30.9 MPa 
3,840.5 meters 
37.7 MPa 
38.9 MPa 
4,785.4 meters 
47 MPa 
48.4 MPa 
11,948 meters 
117.2 MPa 
120.7 MPa 