Hydrostatic Pressure Calculator
Find the hydrostatic pressure at a given depth in a fluid using P = ρgh. Enter the depth in meters or feet and pick the fluid, then choose gauge pressure or absolute (which adds one atmosphere) — results come in kPa, psi, and atmospheres.
Example: with Depth 10 · Depth unit meters · Fluid Fresh water (1000 kg/m³) · Pressure type Gauge (fluid only) → Hydrostatic pressure: 98.07 kPa.
- In psi14.22 psi
- In atmospheres0.97 atm gauge
Computed by the calculator below using its default values. Change any input to see your own numbers.
Fluid pressure grows with depth alone: P = ρgh. Every 10 meters of water adds about one atmosphere, no matter the size or shape of the container.
Why depth is all that matters
The pressure inside a still fluid comes from the weight of everything above a point, and that weight per unit area works out to P = ρgh — density times gravity times depth. Two facts fall out that surprise people. First, the shape of the container is irrelevant: pressure at the bottom of a narrow tube and a wide lake are equal if the depth is equal. Second, pressure acts in all directions, not just down, which is why it squeezes a submarine hull from every side.
The rule of thumb for water is about one atmosphere per 10 meters of depth, or roughly 0.43 psi per foot. Gauge pressure counts only the fluid column; absolute pressure adds the atmosphere pressing on the surface, which is what a diver's body actually experiences. This tool covers static fluid only — moving water in a pipe adds velocity and friction effects that a hydrostatic formula does not capture.
How it’s calculated
Hydrostatic (gauge) pressure P = ρ·g·h, with fluid density ρ in kg/m³, g = 9.80665 m/s², and depth h in meters (feet ×0.3048). Absolute mode adds standard atmospheric pressure, 101,325 Pa. Results convert to kPa (÷1000), psi (÷6894.757), and atm (÷101325).
Assumes a static, incompressible fluid of uniform density and constant g. It ignores fluid motion, temperature-driven density changes, and, for great ocean depths, slight compression of water. Not a pipe-flow or vessel-stress design tool.
Fresh-water gauge pressure by depth
| Depth | Pressure (kPa) | Pressure (psi) |
|---|---|---|
| 1 m (3.3 ft) | 9.8 | 1.42 |
| 3 m (9.8 ft) | 29.4 | 4.27 |
| 10 m (33 ft) | 98.1 | 14.2 |
| 20 m (66 ft) | 196 | 28.4 |
| 100 m (328 ft) | 981 | 142 |
Computed with P = ρgh for fresh water (1000 kg/m³); rounded.
Common mistakes
- Adding atmospheric pressure when a gauge reading is wanted — gauge pressure is the fluid column only.
- Using feet of depth with a metric density without converting depth to meters first.
- Thinking a wider tank raises the pressure; only depth and fluid density set hydrostatic pressure.
- Applying this to flowing water, where velocity and friction change the picture.
Frequently asked questions
What is the hydrostatic pressure formula?
P = ρ·g·h — fluid density times gravity (9.81 m/s²) times depth. It gives gauge pressure; add one atmosphere (101,325 Pa) for absolute pressure.
How much does pressure increase per foot of water?
About 0.433 psi per foot, or roughly 1 atmosphere for every 33 feet (10 meters) of fresh water. Seawater is slightly more because it is denser.
Does the container shape change hydrostatic pressure?
No. Pressure depends only on depth and fluid density, so a thin pipe and a wide tank read the same pressure at the same depth.
What is the difference between gauge and absolute pressure?
Gauge pressure counts only the fluid column; absolute pressure adds the atmosphere pushing on the surface. A diver's body feels absolute pressure.