Hydrostatic Equation Calculator

Solve for

Fluid preset

Pressure unit

Depth or Height

Depth unit

Pressure input

Density

Density unit

Gravity

Gravity unit

Reference pressure

Reference pressure unit

Example Data Table

Fluid	Depth	Density	Gravity	Gauge Pressure	Absolute Pressure
Fresh Water	10 m	1000 kg/m³	9.80665 m/s²	98.07 kPa	199.39 kPa
Seawater	15 m	1025 kg/m³	9.80665 m/s²	150.78 kPa	252.10 kPa
Mercury	0.75 m	13595 kg/m³	9.80665 m/s²	99.99 kPa	201.32 kPa

Formula Used

The hydrostatic equation relates fluid pressure to density, gravity, and vertical depth. It assumes a static fluid and a constant density across the measured depth.

Core Equations

Gauge pressure: P_g = ρgh

Absolute pressure: P_abs = P_ref + ρgh

Depth: h = P_g ÷ (ρg)

Variable Meaning

P_g: Gauge pressure

P_abs: Absolute pressure

P_ref: Surface or reference pressure

ρ: Fluid density

g: Gravitational acceleration

h: Vertical fluid depth or height

How to Use This Calculator

Select the target variable you want to solve.
Choose a fluid preset or enter a custom density.
Enter depth, pressure, gravity, and reference pressure as needed.
Pick the preferred units for pressure, depth, density, and gravity.
Press Calculate to show the result above the form.
Use the export buttons to save the current result as CSV or PDF.

FAQs

1. What does the hydrostatic equation calculate?

It calculates the pressure change caused by a fluid column. You can also rearrange it to solve for depth, density, gravity, or reference pressure.

2. What is the difference between gauge and absolute pressure?

Gauge pressure excludes surrounding atmospheric pressure. Absolute pressure includes the reference pressure acting at the fluid surface, so it is always higher by that reference amount.

3. When is this equation accurate?

It is accurate for fluids at rest and nearly constant density. Large temperature changes, strong compression, or moving fluids require more advanced models.

4. Can I use it for gases?

Yes, but only over small height ranges where density stays nearly constant. For taller gas columns, density variation with height becomes important.

5. Why does pressure increase with depth?

Deeper points support more fluid weight above them. That additional weight creates a larger force per unit area, which means higher pressure.

6. Which density should I enter?

Use the average density of the fluid layer above the point. If the fluid changes significantly with temperature or composition, use a measured or corrected value.

7. What reference pressure should I use?

For open tanks, atmospheric pressure is common. For pressurized vessels, use the gas or surface pressure acting directly on the liquid.

8. Why are unit conversions important here?

The equation is simple, but inconsistent units cause major errors. Converting inputs to one system before calculation keeps the result physically meaningful.