Hydrostatic pressure calculator
Choose the liquid, enter the depth and get the pressure the liquid column adds, and the absolute pressure with one standard atmosphere on the surface. Or enter a gauge pressure to find the depth. Fresh water and seawater are built in; for anything else enter its density.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Choose what to find: the pressure at a depth, or the depth for a pressure.
- Pick fresh water (1000 kg/m³), seawater (1025 kg/m³) or another liquid and enter its density.
- Enter the depth or the gauge pressure, and pick the units. Change g if you are not on Earth.
- Gauge pressure: p = ρ × g × h.
- Absolute pressure: p_abs = p + 101,325 Pa (one standard atmosphere at the surface).
- Depth: h = p ÷ (ρ × g).
Worked example
At 10 m in fresh water: p = 1000 × 9.80665 × 10 = 98,066.5 Pa = 98.0665 kPa. Adding the atmosphere, the absolute pressure is 199.3915 kPa, or 1.9678 atm.
A diver at 100 ft in seawater: p = 1025 × 9.80665 × 30.48 = 306,379.36 Pa = 44.4366 psi gauge.
Tips
- Real seawater density varies with salinity and temperature, roughly 1020 to 1030 kg/m³ at the surface; enter your own value if you need precision.
- Local air pressure changes with weather and altitude; the absolute value here assumes the standard 101,325 Pa.
- Same depth, same pressure: a narrow tube and a wide lake give the same pressure at the same depth.
Frequently asked questions
What is the hydrostatic pressure formula?
p = ρ × g × h, where ρ is the liquid's density in kg/m³, g the gravitational acceleration (9.80665 m/s² standard) and h the depth in metres. The result is in pascals and does not depend on the shape of the container.
What is the difference between gauge and absolute pressure?
Gauge pressure is what the liquid adds, ρgh; it is what most gauges show. Absolute pressure also counts the air above the surface, about 101.3 kPa at sea level. At 10 m in fresh water the gauge pressure is 98.07 kPa and the absolute pressure 199.39 kPa, close to 2 atm.
How much does pressure rise per metre of water?
In fresh water about 9.81 kPa per metre, so roughly one atmosphere every 10.3 m. In seawater, which is denser, a little more, about 10.05 kPa per metre.
Why does a dam get thicker at the bottom?
Pressure grows linearly with depth, so the deepest part of the wall carries the largest load.