Inputs
Set fluid properties and depth. Choose open or pressurized surface.
Example Data Table
Sample values below assume fresh water (998 kg/m³), g = 9.80665 m/s², open surface, and standard atmosphere.
| Depth (m) | ΔP (kPa) | Gauge (kPa) | Absolute (kPa) |
|---|---|---|---|
| 1 | 9.787 | 9.787 | 111.112 |
| 5 | 48.935 | 48.935 | 150.26 |
| 10 | 97.87 | 97.87 | 199.195 |
| 25 | 244.676 | 244.676 | 346.001 |
| 50 | 489.352 | 489.352 | 590.677 |
Formula Used
ρ is fluid density, g is gravity, and h is vertical depth.
How to Use This Calculator
- Select a fluid preset, or choose custom and enter density.
- Enter the vertical depth from the free surface to the point.
- Confirm gravity, especially for non-standard locations.
- Choose surface condition: open or pressurized gauge pressure.
- Set atmospheric pressure for absolute results, then calculate.
- Use the export buttons to save CSV or PDF.
Hydrostatic Pressure Fundamentals
Hydrostatic pressure rises linearly with vertical depth because the fluid weight above a point increases. The calculator applies ΔP = ρgh, where ρ is density, g is gravitational acceleration, and h is depth. In freshwater at 20°C, ρ≈998 kg/m³, so pressure increases about 9.79 kPa per meter. For seawater, ρ≈1025 kg/m³, the gradient is about 10.05 kPa per meter.
Density Inputs and Fluid Presets
Accurate density is the largest driver after depth. Oil, brines, and glycol mixtures can vary widely, often from 800 to 1200 kg/m³ depending on composition. Temperature changes density and can shift pressure by several percent in tall tanks. Use the preset as a starting point, then enter a lab value when design margins are tight. The tool converts g/cm³ and lb/ft³ to SI internally for consistent computation.
Depth, Head, and Unit Control
Depth must be vertical, not pipe length or sloped distance. When depth is entered in feet or inches, the calculator converts to meters before computing pressure. The “pressure head” result reports the equivalent height of the same fluid that produces the gauge pressure: H = Pgauge/(ρg). For open surfaces, head equals depth, while pressurized surfaces add extra head above the free-surface level.
Surface Condition and Pressure Reference
Engineering specifications often require both gauge and absolute pressure. Gauge pressure is referenced to local atmosphere and is typical for pumps, valves, and structural checks on small plates. Absolute pressure adds atmospheric pressure and is required for vapor pressure, cavitation, and gas-space calculations. If the surface is pressurized, the entered surface gauge pressure is added to the hydrostatic rise to obtain Pgauge at depth.
Design Use Cases and Quick Validation
Use the results to size tank walls, check manway covers, estimate sensor ranges, and verify test pressures. For deep wells, confirm material limits and include safety factors for transient surges also. As a quick check, 10 m of water produces roughly 98 kPa gauge, close to 1 bar. A 0.01 m² plate at 200 kPa gauge sees about 2000 N of force under the uniform-pressure approximation. For large gates, pressure varies with depth, so integrate the pressure distribution for total force and centroid location.
FAQs
1) What is hydrostatic pressure and when does it apply?
It is the pressure created by a fluid at rest due to its weight. It applies in tanks, reservoirs, pipes with static columns, and any situation where the fluid velocity is negligible at the point of interest.
2) Why do you show both gauge and absolute pressure?
Gauge pressure is relative to local atmosphere and is common for equipment ratings. Absolute pressure includes atmospheric pressure and is needed for cavitation checks, gas spaces, and calculations involving vapor pressure.
3) Which density value should I enter for best results?
Use the density at operating temperature and composition. For mixtures or brines, use a measured value when possible. If only a range is known, run high and low densities to bracket pressure.
4) Why can pressure head differ from depth in this tool?
Head equals depth only for an open surface with zero surface gauge pressure. If the surface is pressurized, the added surface gauge pressure increases Pgauge, producing an equivalent head greater than the entered depth.
5) Can I use this calculator for gases or two‑phase flow?
It is intended for liquids where density is nearly constant with depth. For gases, density changes significantly with pressure and temperature, so a compressible model is required for reliable results.
6) How should I interpret the force-on-area result?
It uses F = Pgauge × A, which is valid when pressure is nearly uniform over the area. For large vertical gates, pressure varies with depth, so integrate the distribution to find total force and line of action.