The fluid pressure calculator computes hydrostatic pressure at depth using P = ρgh (gauge) or P = P₀ + ρgh (absolute). Choose from 9 common fluids or enter a custom density. Results in Pa, kPa, atm, and psi simultaneously.
Inputs
Every 33 ft (10 m) of water ≈ 1 additional atm
Results
Enter values and click Calculate
How to Use the Fluid Pressure Calculator
Fluid pressure increases with depth because the weight of the fluid above presses down. The formula P = ρgh gives gauge pressure (pressure above atmospheric). To find absolute pressure, add atmospheric pressure: P_abs = P_atm + ρgh.
Example: Swimming Pool at 3 Meters
A swimmer at the bottom of a 3 m pool (fresh water, ρ = 1000 kg/m³): gauge pressure = 1000 × 9.81 × 3 = 29,430 Pa ≈ 0.29 atm ≈ 4.27 psi. Absolute pressure = 101,325 + 29,430 = 130,755 Pa ≈ 1.29 atm. This is the pressure their ears experience — roughly equivalent to plugging their ears and someone pushing with about 4.27 psi from outside.
Gauge vs Absolute Pressure
Gauge pressure is what your tire pressure gauge reads — it measures pressure above the ~14.7 psi (1 atm) atmospheric baseline. Absolute pressure is the total pressure in the fluid, including the atmospheric contribution. Scuba diving depth ratings use gauge pressure; engineering calculations often need absolute pressure.
Force on a Surface
Enter an area to find the total force exerted at that depth: F = P × A. For a 1 m² panel at the bottom of a 5 m tank (fresh water): gauge pressure = 49,050 Pa, force = 49,050 × 1 = 49,050 N ≈ 5 tonnes. This matters for dam design, submarine hull calculations, and underwater structures.
Using Custom Fluids
Select "Custom density" and enter any fluid's density in kg/m³. Mercury (13,600 kg/m³) exerts 13.6× more pressure than water at the same depth. Gasoline (680 kg/m³) exerts 68% as much pressure as water.
FAQ
What is hydrostatic pressure?
Hydrostatic pressure is the pressure exerted by a static fluid at a given depth due to gravity. It follows Pascal's law: P = ρgh, where ρ is fluid density (kg/m³), g is gravitational acceleration (9.81 m/s²), and h is depth (m). Pressure increases linearly with depth — every 10 m of water adds about 1 atm (101.3 kPa).
What is the pressure at 10 meters underwater?
At 10 m in fresh water: gauge pressure = 1000 × 9.81 × 10 = 98,100 Pa ≈ 0.968 atm ≈ 14.2 psi. Absolute pressure including 1 atm surface pressure ≈ 199,425 Pa ≈ 1.97 atm ≈ 29 psi. In sea water (1025 kg/m³), pressure is about 2.5% higher.
What is gauge pressure vs absolute pressure?
Gauge pressure measures pressure relative to atmospheric pressure (ignoring the ~101.3 kPa above you). Absolute pressure is gauge pressure plus atmospheric pressure. Diving depth ratings and tire pressure use gauge pressure. Vacuum calculations and thermodynamic equations require absolute pressure.
How deep can a human diver go?
A recreational scuba diver typically dives to 18–40 m. At 40 m in seawater: gauge pressure = 1025 × 9.81 × 40 ≈ 402,390 Pa ≈ 4 atm ≈ 58 psi. The absolute pressure is about 5 atm. This is why nitrogen narcosis becomes a concern — the partial pressure of nitrogen in air increases proportionally with depth.
Is this calculator free?
Yes, completely free with no signup required. All calculations run in your browser.
Is my data private?
Yes. All calculations run locally. Nothing is transmitted to any server.
Why is mercury used in barometers?
Mercury's high density (13,600 kg/m³) means standard atmospheric pressure (101,325 Pa) only requires a 760 mm mercury column instead of about 10.3 m of water. This makes mercury barometers compact. Modern barometers use aneroid capsules or electronic sensors, but 'mmHg' (millimeters of mercury) persists as a pressure unit in medicine.