Hydrostatic Pressure Calculator Formula
Understand the math behind the hydrostatic pressure calculator. Each variable explained with a worked example.
Formulas Used
Gauge Pressure
gauge_p = density * 9.81 * depth / 1000Absolute Pressure
absolute_p = atm_pressure + density * 9.81 * depth / 1000Variables
| Variable | Description | Default |
|---|---|---|
density | Fluid Density (rho)(kg/m^3) | 1000 |
depth | Depth Below Surface (h)(m) | 10 |
atm_pressure | Atmospheric Pressure(kPa) | 101.325 |
How It Works
Hydrostatic Pressure
Pressure in a static fluid increases linearly with depth due to the weight of the fluid above.
Formula
P_gauge = rho g h
P_absolute = P_atm + rho g h
where rho is fluid density, g = 9.81 m/s^2, and h is the depth below the free surface. For water, pressure increases by approximately 9.81 kPa (about 1 atmosphere per 10.33 m) for each metre of depth.
Worked Example
10 m below the surface of fresh water at standard atmospheric pressure.
- 01Gauge pressure = 1000 x 9.81 x 10 = 98,100 Pa = 98.10 kPa
- 02Absolute pressure = 101.325 + 98.10 = 199.43 kPa
- 03This is approximately 2 atmospheres absolute.
Frequently Asked Questions
What is the difference between gauge and absolute pressure?
Gauge pressure is measured relative to atmospheric pressure (reads zero at surface). Absolute pressure includes atmospheric pressure. Most pressure gauges read gauge pressure; add atmospheric pressure for absolute.
Does the shape of the container affect hydrostatic pressure?
No. Hydrostatic pressure depends only on depth, fluid density, and gravity - not on the container shape. This is known as Pascal's law or the hydrostatic paradox.
How deep is one atmosphere of water?
One atmosphere (101.325 kPa) of gauge pressure corresponds to 101,325 / (1000 x 9.81) = 10.33 m of fresh water or about 9.9 m of seawater.
Learn More
Guide
Hydraulic System Basics: Pressure, Flow, Cylinders, and Circuit Design
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