Calculate hydrostatic pressure, gauge pressure, and absolute pressure at any fluid depth. Supports water, oil, mercury, and custom fluids.
The Fluid Pressure Calculator determines the pressure exerted by a column of fluid at any depth using the hydrostatic pressure equation P = ρgh. This fundamental relationship governs water supply systems, hydraulic equipment, dam design, diving safety, and countless engineering applications. It is a practical way to estimate loading before you commit to a tank, pipe, or hydraulic design. It also gives you a quick check on how much pressure changes when the depth or fluid density changes.
Hydrostatic pressure increases linearly with depth and is independent of container shape — a phenomenon known as the hydrostatic paradox. The calculator handles atmospheric pressure addition for absolute pressure, supports multiple fluid types with their densities, and converts between pressure units (psi, kPa, bar, atm, mmHg, inH₂O).
Enter the fluid type and depth to calculate gauge pressure, absolute pressure, and force on a specified area. Compare pressures across different fluids and depths with the reference table.
Use this calculator when you need pressure at depth, not just a unit conversion. It is useful for tank design, diving checks, hydraulic systems, and any case where fluid density and depth determine the load. That makes it easier to size hardware and compare fluids without doing the same depth math repeatedly.
P_gauge = ρ × g × h. P_absolute = P_atm + ρgh. Force = P × A. Where ρ = fluid density (kg/m³), g = 9.81 m/s², h = depth (m), P_atm = 101,325 Pa (1 atm). Water: ρ = 997 kg/m³ at 25°C.
Result: 97.8 kPa gauge / 199.1 kPa absolute
P = 997 × 9.81 × 10 = 97,806 Pa ≈ 97.8 kPa gauge. Adding atmospheric pressure: 97.8 + 101.3 = 199.1 kPa absolute. This equals roughly 1 additional atmosphere, which matches the classic "every 10m adds 1 atm" rule for divers.
Hydrostatic pressure calculations are essential for designing dams (force on the face increases with the square of height), water towers (pressure at ground level = height × density × g), submarine hulls (must withstand crushing depth pressures), and underground pipes (soil and water pressure combine). The trapezoidal pressure distribution on a vertical wall produces a resultant force acting at 1/3 of the height from the base.
Engineers work with many pressure units: 1 atm = 101.325 kPa = 14.696 psi = 1.01325 bar = 760 mmHg = 29.92 inHg = 407.2 inH₂O = 10.33 mH₂O. Industrial processes often use barg (bar gauge) or psig (psi gauge). Scientific work uses pascals (Pa) or kilopascals. Weather reports use millibars (mbar) or inches of mercury (inHg).
Pascal's principle enables hydraulic presses, car jacks, brake systems, and heavy equipment. A hydraulic cylinder with a 10:1 area ratio multiplies input force by 10×. A car brake system might use a 1" master cylinder pressing fluid to four 2.5" wheel cylinders, multiplying pedal force by 6.25× per wheel — enough to stop a 4,000 lb vehicle from highway speed.
Gauge pressure is relative to atmospheric pressure (what a typical pressure gauge reads). Absolute pressure includes atmospheric pressure. At sea level, P_abs = P_gauge + 101.325 kPa (14.7 psi). A tire at 32 psi gauge is 46.7 psi absolute.
Each foot of water exerts 0.433 psi (0.305 m of water = 2.989 kPa). At 100 feet deep, water pressure is 43.3 psi gauge. Remember this: 2.31 feet of water = 1 psi.
This is the hydrostatic paradox. A narrow tube and a wide tank with the same water height produce the same pressure at any depth. Pressure depends only on depth, density, and gravity — not on the volume of fluid above. The container walls redirect forces.
The average ocean depth is about 3,688m, producing roughly 370 atm (5,440 psi). The Mariana Trench at 10,994m reaches about 1,086 atm (15,960 psi). At these pressures, water compresses by about 5%.
Temperature changes fluid density, indirectly affecting pressure. Water density varies from 999.8 kg/m³ at 4°C to 958.4 kg/m³ at 100°C — about a 4% difference. For most applications below 50°C, temperature effects are negligible.
Pascal's principle states that pressure applied to a confined fluid is transmitted equally in all directions. This is the basis of hydraulic systems — a small force on a small piston creates a large force on a large piston, proportional to the area ratio.