Hydrostatic Pressure Calculator
Choose a fluid and a depth to get the pressure from the fluid column. Add the atmosphere to get absolute pressure.
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Formula
P = ρ × g × h
- ρ is the fluid density in kg/m³: fresh water 1000, sea water 1025, oil 900, mercury 13,595.1.
- g = 9.80665 m/s² (standard gravity) and h is the depth in metres.
- Absolute pressure = P + 101,325 Pa (one standard atmosphere).
Worked example
10 m of fresh water:
P = 1000 × 9.80665 × 10 = 98,066.5 Pa
That is 98.07 kPa, 0.981 bar or 14.22 psi gauge. Adding the atmosphere gives 199,391.5 Pa, about 1.968 atm absolute.
Assumptions: the fluid density is constant with depth (it is nearly constant for liquids), g is the standard value and the fluid is at rest.
Frequently asked questions
What is the hydrostatic pressure formula?
P = ρ × g × h, where ρ is the fluid density, g = 9.80665 m/s² and h is the depth. At 10 m in fresh water: 1000 × 9.80665 × 10 = 98,066.5 Pa, about 98 kPa.
What is the difference between gauge and absolute pressure?
Gauge pressure counts only the fluid column. Absolute pressure also adds the atmosphere above it, 101,325 Pa. At 10 m deep in water the absolute pressure is 98,066.5 + 101,325 = 199,391.5 Pa, nearly 2 atm.
Why does pressure not depend on the width of the container?
Only the vertical height of the fluid above a point matters, not the shape or volume. A narrow tube and a wide lake 10 m deep give the same pressure at the bottom.
How is 760 mm of mercury related to one atmosphere?
A column of mercury 0.76 m high gives 13,595.1 × 9.80665 × 0.76 ≈ 101,325 Pa, which is one standard atmosphere. That is why barometers and blood pressure are quoted in mmHg.