📖 How To Use
How to Use This Calculator
Calculating hydrostatic water column pressure takes three steps:
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Enter the water column height
This is the vertical distance from the water surface down to the point where you need the pressure — not the length of any pipe. Choose your unit: metres, feet, cm, inches, or mm.
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Select your fluid type
Fresh water, seawater, diesel, cooking oil, milk — or enter a custom density in kg/m³ if you're working with a non-standard fluid. Density directly scales the result.
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Adjust gravity if needed (optional)
Defaults to 9.81 m/s² (standard Earth). Change this if you need calculations for a different altitude or planet.
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Read your results
Primary result is PSI — the unit most plumbing specs use. Secondary outputs include bar, kPa, Pa, metres of head, atmospheres, and mmHg. Copy or print for your records.
Important: This calculator gives gauge pressure — pressure above atmospheric. Absolute pressure = gauge pressure + 101.325 kPa (1 atm). For most plumbing and irrigation applications, gauge pressure is what you need.
📐 The Formula
Water Column Pressure Formula
Hydrostatic pressure from a static water column is one of the most fundamental equations in fluid mechanics:
P = ρ × g × h
Where:
P = pressure in Pascals (Pa)
ρ = fluid density in kg/m³ (fresh water = 1,000)
g = gravitational acceleration = 9.81 m/s²
h = height of water column in metres
For fresh water at standard gravity, this simplifies to roughly 9,810 Pa per metre (or about 0.1 bar/m, or 1.422 PSI/ft). The table below gives quick reference values:
Pressure per Metre of Fresh Water Column
| Height | Pa | kPa | PSI | bar | m Head |
|---|
| 0.5 m | 4,905 | 4.905 | 0.711 | 0.0491 | 0.5 |
| 1 m | 9,810 | 9.810 | 1.422 | 0.0981 | 1.0 |
| 2 m | 19,620 | 19.620 | 2.845 | 0.1962 | 2.0 |
| 3 m | 29,430 | 29.430 | 4.267 | 0.2943 | 3.0 |
| 5 m | 49,050 | 49.050 | 7.112 | 0.4905 | 5.0 |
| 10 m | 98,100 | 98.100 | 14.223 | 0.9810 | 10.0 |
| 15 m | 147,150 | 147.15 | 21.335 | 1.4715 | 15.0 |
| 20 m | 196,200 | 196.20 | 28.447 | 1.9620 | 20.0 |
Unit Conversion Reference
| From | To PSI | To bar | To kPa |
|---|
| 1 Pa | 0.000145 | 0.00001 | 0.001 |
| 1 kPa | 0.14504 | 0.01 | 1 |
| 1 bar | 14.504 | 1 | 100 |
| 1 PSI | 1 | 0.06895 | 6.895 |
| 1 atm | 14.696 | 1.01325 | 101.325 |
❓ FAQ
Frequently Asked Questions
How do I calculate water pressure from height?
Use the formula P = ρ × g × h. For fresh water: pressure in kPa equals height in metres × 9.81. So a 10-metre water column produces 98.1 kPa or about 14.2 PSI. This calculator does the full conversion automatically for every pressure unit.
What is the minimum tank height needed for good shower pressure?
Most modern showers require at least 1 bar (about 10 metres of head). Budget thermostatic valves and power showers typically need 1.5–3 bar. A gravity-fed rooftop tank at 3–5 m above the showerhead — common in many homes — gives only 0.3–0.5 bar, which is why a pump booster is often added. Use our Minimum Tank Height for Shower Pressure Calculator for a dedicated tool.
Is this gauge pressure or absolute pressure?
This calculator gives gauge pressure — pressure above atmospheric. Absolute pressure = gauge pressure + 101.325 kPa. For plumbing, pump specs, and pressure ratings, gauge pressure is almost always what's required. Absolute pressure matters in vacuum systems and scientific applications.
Does the pipe diameter affect water column pressure?
No — hydrostatic pressure depends only on vertical height and fluid density, not pipe diameter. A 10-metre column in a 15 mm pipe creates exactly the same pressure as a 10-metre column in a 200 mm pipe. Diameter affects flow rate and friction losses, not static pressure.
What is metres of head in water pressure terms?
Metres of head (m H₂O) is a way to express pressure as the equivalent height of a water column. 1 metre of head = 9.81 kPa = 0.0981 bar = 1.422 PSI. It's widely used in pump specifications because it directly describes how high a pump can lift water against gravity.
How does seawater pressure compare to fresh water?
Seawater is about 2.5% denser than fresh water (1,025 vs 1,000 kg/m³). A 10-metre seawater column gives ~100.5 kPa versus 98.1 kPa for fresh water — about 2.5% more pressure. Select "Seawater" in the fluid type picker to get accurate values for saltwater storage or offshore applications.
Can I use this calculator for water pressure from an underground tank?
Yes. Enter the vertical distance from the water surface in the underground tank down to the outlet or pump suction point. If the outlet is above the water surface, the pressure will be negative — meaning you'll need a pump to lift the water. The formula works the same way for any vertical height difference.
What PSI does a rooftop water tank typically produce?
A typical single-storey house has the rooftop tank 2–4 metres above the highest outlet, giving just 0.28–0.57 bar (4–8 PSI). Two storeys might add another 3–4 metres. Multi-storey buildings with tanks on the roof may achieve 10–15 m of head (1–1.5 bar / 14–22 PSI). Many modern fixtures need more, hence the widespread use of pressure-boosting pumps.