What next?
Static pressure is one part of a fluid problem. Flow is the other.
How to use this calculator
- Enter the fluid density (ρ), or tap the water preset.
- Enter the depth (h) below the surface, in metres.
- Read the pressure due to the fluid above.
What your result means
This is the gauge pressure from the weight of fluid above a point — the deeper you go, the more fluid pushes down. It uses g = 9.81 m/s² and ignores the atmospheric pressure pressing on the surface.
Why this one is different
What comes back is gauge pressure — the liquid alone — and the absolute figure is given with it, atmospheric pressure added, because which one a gauge reads is where this calculation usually goes astray. The working also notes what the answer does not depend on: the shape or the width of the container, only depth, density and gravity.
A thin tube pushes as hard as a wide lake
Hydrostatic pressure depends only on depth, density and gravity — never on the shape or width of the container. A metre of water in a drinking straw presses on its base with exactly the same pressure as a metre-deep lake. This is the hydrostatic paradox.
How it works
Fluid pressure equals density times gravity times depth. Density sets how heavy the fluid is, gravity pulls it down, and depth stacks up more of it — so pressure rises linearly the further down you go.
Formula
Worked example
Pressure at 3 m depth in fresh water (ρ = 1,000 kg/m³):
P = 1,000 × 9.81 × 3
P = 29,430 Pa (29.43 kPa)
That is gauge pressure. Absolute pressure at that depth is 29.43 + 101.33 = 130.76 kPa. Sea water (about 1,025 kg/m³) gives roughly 2.5% more.
Depth sets the pressure, not the volume
Hydrostatic pressure is ρgh — density times gravity times depth — and the shape or volume of the container does not appear in it. A narrow tube of water one metre tall exerts exactly the same pressure at its base as a swimming pool of the same depth. This is the hydrostatic paradox, and it explains why a tall thin standpipe can burst a tank, why header tanks are mounted high rather than made large, and why dam thickness is driven by depth rather than by the reservoir’s surface area.
Gauge pressure and absolute pressure
Most instruments read gauge pressure: pressure relative to the surrounding atmosphere. Absolute pressure adds atmospheric pressure, about 101.3 kPa at sea level. The distinction is usually harmless and occasionally critical — gas law calculations, pump cavitation checks and anything involving vacuum must use absolute values, while structural loading on a tank wall is a gauge quantity because the atmosphere pushes on both sides. Note also that fluid density varies with temperature, so a hot-water column exerts slightly less pressure than a cold one of the same height.
Frequently asked questions
Does container shape change the pressure?＋
No. Only depth, fluid density and gravity matter. A narrow tube and a wide tank filled to the same depth give the same pressure at the bottom.
Is this absolute or gauge pressure?＋
It is the gauge pressure from the fluid alone. To get absolute pressure, add atmospheric pressure (about 101 kPa at sea level).
How deep is one atmosphere of water?＋
About 10.33 m of fresh water, since 101,325 Pa divided by 1,000 × 9.81 gives 10.33. That is the origin of the diving rule of thumb that pressure roughly doubles at 10 m: you have added one atmosphere of water on top of the one already in the air.
How does pressure relate to pump head?＋
Head is pressure expressed as a height of the fluid being pumped. Ten metres of water head is about 0.98 bar, which is why pump curves are quoted in metres rather than pressure units.
What is the difference between static and dynamic pressure?＋
Static pressure comes from depth alone and exists whether or not the fluid moves. Dynamic pressure comes from velocity. Bernoulli's principle describes how a flow trades one for the other.
Does the fluid's density matter more than depth?＋
Both enter the equation equally, since pressure is density times gravity times depth. Mercury is 13.6 times denser than water, so a column a thirteenth as tall produces the same pressure.
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Assumptions & limitations
Engineering formulas are exact; the situations they model are not. Read your result with these limits in mind:
- Hydrostatic only — the fluid is assumed to be at rest. Moving fluid adds dynamic pressure, which this does not include.
- Assumes constant density, which is fine for liquids but wrong for gases over any significant height.
- Depth is measured vertically from the free surface. The shape or width of the container makes no difference.
- Uses g = 9.81 m/s². Local gravity varies by about ±0.3% across the Earth's surface.