Pressure Calculator

Pressure (P) equals force (F) divided by area (A): P = F/A. This tells us how concentrated a force is over a surface. A small area results in higher pressure. The SI unit is Pascal (Pa), where 1 Pa = 1 N/m2. A force of 100 N spread over 1 m2 creates 100 Pa of pressure.

Hydrostatic pressure is the pressure exerted by a fluid at rest due to gravity. It is calculated as P = pgh, where p is fluid density, g is gravitational acceleration, and h is depth. For water (p = 1000 kg/m3), pressure increases by about 9,800 Pa (0.097 atm) per meter of depth.

Absolute pressure is measured relative to a perfect vacuum (zero pressure). Gauge pressure is measured relative to atmospheric pressure. Gauge pressure = Absolute pressure - Atmospheric pressure. A tire gauge reading 32 psi is gauge pressure; absolute pressure would be 32 + 14.7 = 46.7 psi.

Atmospheric pressure is the force per unit area exerted by the weight of air above. At sea level, it equals 101,325 Pa (1 atm = 14.7 psi = 760 mmHg). This means a column of air above 1 m2 weighs about 10,330 kg! Atmospheric pressure decreases with altitude.

Common conversions: 1 atm = 101,325 Pa = 101.325 kPa = 1.01325 bar = 14.696 psi = 760 mmHg = 760 torr. To convert, multiply by the appropriate factor. For example, 2 atm = 2 x 101,325 = 202,650 Pa, or 2 x 14.696 = 29.39 psi.

Water is much denser than air (p = 1000 kg/m3 vs 1.2 kg/m3). Using P = pgh, every 10 meters of water depth adds about 1 atmosphere of pressure. At 30 meters, a diver experiences 4 atmospheres total (1 atmospheric + 3 from water), causing nitrogen narcosis and requiring decompression.

Pressure increases linearly with depth in an incompressible fluid: P = pgh + P0, where P0 is surface pressure. For water, this is approximately 10 kPa per meter (or 1 atm per 10.3 m). This is why dams are thicker at the bottom and submarine hulls must withstand enormous pressures.

Pressure = Force/Area. A sharp point has a tiny area, so even a small force creates enormous pressure. A needle with 0.01 mm2 tip area and 1 N force creates P = 1 / (0.01 x 10^-6) = 100 million Pa! This is why a light press with a needle can pierce skin that withstands much larger distributed forces.