📖 How To Use
How to Use This Hydrostatic Pressure Calculator
Calculating hydrostatic pressure takes under 30 seconds:
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Enter the fluid depth or height
Measure the vertical distance from the water surface down to the point where you need to know the pressure. Use the unit selector to match your measurement (metres, feet, cm, mm, or inches).
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Select your fluid type
Use the quick-select dropdown to pick fresh water, seawater, diesel, or another common fluid. This automatically fills the density field. For unusual fluids, choose "Custom" and enter the density in kg/m³ manually.
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Hit Calculate
Results appear instantly in PSI, Bar, kPa, Pascal, metres water column (mWC), and atmospheres. Copy or print the full output with one click.
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Check the pressure diagram
The visual shows the depth-pressure relationship — the longer the water column, the higher the gauge pressure at the bottom.
Important: This calculator gives gauge pressure (pressure above atmospheric). Absolute pressure = gauge pressure + 101.325 kPa (1 atm). For most tank and pipe engineering problems, gauge pressure is what you need.
📐 The Formula
Hydrostatic Pressure Formula
Hydrostatic pressure depends on three things: fluid density, gravitational acceleration, and depth:
P = ρ × g × h
P = hydrostatic pressure (Pascal, Pa)
ρ = fluid density (kg/m³)
g = gravitational acceleration = 9.81 m/s²
h = depth below the fluid surface (metres)
The result in Pascal can then be converted to any other pressure unit. This calculator performs all conversions automatically.
Unit Conversion Reference
| Unit | Equals Pascal | From Pascal |
|---|
| 1 Pascal (Pa) | 1 Pa | × 1 |
| 1 Kilopascal (kPa) | 1,000 Pa | ÷ 1,000 |
| 1 Bar | 100,000 Pa | ÷ 100,000 |
| 1 PSI | 6,894.76 Pa | ÷ 6,894.76 |
| 1 Atmosphere (atm) | 101,325 Pa | ÷ 101,325 |
| 1 mmHg (Torr) | 133.322 Pa | ÷ 133.322 |
| 1 m Water Column (mWC) | 9,806.65 Pa | ÷ 9,806.65 |
Pressure vs. Depth Reference (Fresh Water)
| Depth | Pascal (Pa) | kPa | PSI | Bar |
|---|
| 1 m | 9,810 | 9.81 | 1.42 | 0.098 |
| 5 m | 49,050 | 49.05 | 7.11 | 0.491 |
| 10 m | 98,100 | 98.1 | 14.22 | 0.981 |
| 20 m | 196,200 | 196.2 | 28.45 | 1.962 |
| 50 m | 490,500 | 490.5 | 71.12 | 4.905 |
| 100 m | 981,000 | 981 | 142.2 | 9.81 |
❓ FAQ
Frequently Asked Questions
What is hydrostatic pressure?
Hydrostatic pressure is the pressure exerted by a fluid at rest due to gravity. It increases linearly with depth — every additional metre of fresh water adds approximately 9,810 Pa (or about 1.42 PSI) of pressure. It does not depend on the shape of the container, only on the depth of the fluid.
How do I calculate water pressure from tank height?
Use the formula P = ρ × g × h, where ρ is the water density (1,000 kg/m³ for fresh water), g is 9.81 m/s², and h is the vertical height in metres. For example, a 5-metre-tall full tank produces a gauge pressure of 49,050 Pa (49.05 kPa or about 7.1 PSI) at its base. This calculator does all the arithmetic for you.
What is the difference between gauge pressure and absolute pressure?
Gauge pressure is the pressure relative to atmospheric pressure (what most pressure gauges show). Absolute pressure includes the weight of the atmosphere on top — it equals gauge pressure + 101.325 kPa (1 atm). For tank and pipe design, gauge pressure is almost always the relevant figure. This calculator outputs gauge pressure.
Does tank shape affect hydrostatic pressure?
No — this is a common misconception. Hydrostatic pressure at any given depth depends only on the fluid density and the vertical height of fluid above that point. A narrow tank and a wide lake produce identical pressure at the same depth. This is known as the hydrostatic paradox.
How much pressure does a rooftop water tank generate?
A tank mounted 5 metres above the tap delivers roughly 49 kPa (0.49 bar or 7.1 PSI) of static pressure. Most shower heads need at least 10–20 kPa to function — so even a tank just 1–2 metres above often provides enough gravity-feed pressure for basic fixtures. Use our Minimum Tank Height for Shower Pressure Calculator for exact requirements.
Can I use this calculator for fluids other than water?
Yes — select the fluid from the quick-pick dropdown (seawater, diesel, cooking oil, milk, petrol) or enter any custom density in kg/m³. The formula and all outputs adjust automatically. For example, seawater at 1,025 kg/m³ produces about 2.5% more pressure than fresh water at the same depth.
What is metres water column (mWC) and when is it used?
Metres water column (mWC) is a pressure unit commonly used in plumbing and HVAC. 1 mWC equals the pressure exerted by 1 metre of fresh water — approximately 9,807 Pa or 0.098 bar. Pump datasheets often specify head pressure in metres, making mWC a convenient unit for tank and pump system design.