Does this formula give gauge or absolute pressure?

P = rho*g*h gives gauge pressure — the pressure above atmospheric. To get absolute pressure, add atmospheric pressure: P_abs = P_atm + rho*g*h, where P_atm is approximately 101,325 Pa at sea level.

Why does pressure depend on depth but not on the horizontal area of the container?

Hydrostatic pressure depends only on the weight of the fluid column above the point in question, which is determined by depth and fluid density. The shape or width of the container does not change the pressure at a given depth.

What is g in the formula and what value should I use?

g is the local gravitational acceleration. On Earth's surface use g = 9.81 m/s^2. At altitude or for precise engineering work, use the local measured value. On the Moon you would use 1.62 m/s^2.

Hydrostatic Pressure Calculator

Calculate the pressure at a given depth in a fluid using P = rho * g * h. Enter fluid density in kg/m^3, gravitational acceleration, and depth in metres. Returns gauge pressure in pascals. Perfect for hydraulics and fluid statics.

By AbraCalc Editorial Team · Reviewed by AbraCalc Methodology Review · Last reviewed: 2026-06-25

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How to use this tool

Enter fluid density (ρ), gravity (g) and depth (h) in the fields above.
Results update instantly as you type — or click Calculate.
Read your hydrostatic pressure and the full breakdown beneath it.

Formula

P = rho * g * h

How it works

Hydrostatic gauge pressure at depth h in a fluid of density ρ under gravity g is P = ρgh. This is the extra pressure above the surface pressure.

Worked examples

Swimming pool at 10 m

Mercury barometer

Common mistakes to avoid

Using the wrong fluid density — water is approximately 1000 kg/m^3 but seawater is about 1025 kg/m^3 and hydraulic oil around 870 kg/m^3; using 1000 for all fluids introduces error.
Entering depth in centimetres or feet instead of metres without converting, producing a pressure answer off by a factor of 100 or 0.305.
Forgetting to add atmospheric pressure (101,325 Pa) when absolute pressure is needed — rho*g*h gives gauge pressure only.

Key terms

Frequently asked questions

Does this formula give gauge or absolute pressure?: P = rho*g*h gives gauge pressure — the pressure above atmospheric. To get absolute pressure, add atmospheric pressure: P_abs = P_atm + rho*g*h, where P_atm is approximately 101,325 Pa at sea level.
Why does pressure depend on depth but not on the horizontal area of the container?: Hydrostatic pressure depends only on the weight of the fluid column above the point in question, which is determined by depth and fluid density. The shape or width of the container does not change the pressure at a given depth.
What is g in the formula and what value should I use?: g is the local gravitational acceleration. On Earth's surface use g = 9.81 m/s^2. At altitude or for precise engineering work, use the local measured value. On the Moon you would use 1.62 m/s^2.