Underwater Pressure Calculator

Gauge pressure at depth = water density * gravitational acceleration * depth (P = rho * g * h). Absolute pressure = gauge pressure + atmospheric pressure (101,325 Pa at sea level). For seawater (density 1,025 kg/m3): P gauge (Pa) = 1025 * 9.81 * depth (m). This formula comes directly from fluid statics principles published by NIST.

In seawater, pressure increases by approximately 1 atmosphere (14.7 psi or 101.3 kPa) for every 10 metres (33 feet) of depth. At 10 m depth, absolute pressure is 2 atm (1 atm surface + 1 atm water). At 30 m depth, absolute pressure is 4 atm. This relationship is why scuba divers must equalise their ears as they descend.

Increased pressure compresses gas in the body's air spaces (lungs, sinuses, ears, intestines). Divers must equalise the air spaces to prevent barotrauma. The increased partial pressure of nitrogen at depth also causes more nitrogen to dissolve into blood and tissues, which must be safely eliminated during ascent to prevent decompression sickness.

Gauge pressure is the pressure relative to atmospheric pressure at the surface (so at the surface, gauge pressure is zero). Absolute pressure includes atmospheric pressure. At 10 m depth in seawater: gauge pressure = approximately 1 atm (100 kPa); absolute pressure = approximately 2 atm (202 kPa). Dive computers and pressure ratings typically use gauge pressure.

Yes. Saltwater (density approximately 1,025 kg/m3) is denser than freshwater (1,000 kg/m3). At 10 m depth: freshwater gauge pressure = 98.1 kPa (0.968 atm); saltwater gauge pressure = 100.5 kPa (0.992 atm). The difference is about 2.5%, which is noticeable for precision dive planning but relatively minor for recreational diving.