📖 How To Use

How to Use This Calculator

Calculating hydrostatic water column pressure takes three steps:

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: feet, inches, metres, cm or mm.
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.
Adjust gravity if needed (optional) Defaults to standard gravity, 9.80665 m/s². Real gravity on Earth only varies from about 9.78 m/s² at the equator to 9.83 m/s² at the poles — under 0.3% — so leave it unless you need lab-grade precision or are working for another planet.
Read your results Primary result is PSI — the unit US plumbing specs use. Secondary outputs include bar, kPa, Pa, metres of head, atmospheres and mmHg; the note under the results adds feet and inches of water column and the working in US units. Copy or print for your records.

Important: This calculator gives gauge pressure — pressure above atmospheric. Absolute pressure = gauge pressure + about 14.7 psi (101.325 kPa, 1 atm) at sea level. For most plumbing and irrigation applications, gauge pressure is what you need. It is also static pressure: once water flows, pipe friction takes some of it.

📐 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 = standard gravity = 9.80665 m/s² (9.81 for hand sums)
h = height of water column in metres

For fresh water at standard gravity, this simplifies to roughly 9,810 Pa per metre (about 0.098 bar or 1.422 psi per metre). In US units it is 0.433 psi per foot — or 2.31 ft of water for every 1 psi. The tables below give 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

Pressure per Foot of Fresh Water Column

Height	Metres	PSI	kPa	bar	in WC
1 ft	0.30 m	0.43	3.0	0.030	12
2 ft	0.61 m	0.87	6.0	0.060	24
3 ft	0.91 m	1.30	9.0	0.090	36
5 ft	1.52 m	2.17	14.9	0.149	60
10 ft	3.05 m	4.34	29.9	0.299	120
20 ft	6.10 m	8.67	59.8	0.598	240
33.9 ft	10.33 m	14.70	101.3	1.013	407
50 ft	15.24 m	21.68	149.5	1.495	600
100 ft	30.48 m	43.35	298.9	2.989	1,200

A 33.9 ft (10.3 m) column of water equals one standard atmosphere — which is also why a pump at the surface can never pull water up more than about 33 ft by suction, and in practice only about 20–25 ft.

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

💡 Use Cases

When to Use a Water Column Pressure Calculator

🚿

Shower & Tap Pressure

A tank whose water level sits 10 ft (3 m) above a shower gives about 4.3 psi (0.29 bar) — enough for a shower made for low-pressure gravity systems, but weak for most standard fixtures, which are designed around far higher pressures.

🌾

Gravity Irrigation

Drip tubing makers commonly recommend about 8–15 psi (0.55–1 bar), which needs roughly 18–35 ft (5.5–10.5 m) of head. Ultra-low-pressure drip designs can run from a tank only 2–5 ft up. Use this calculator to plan your tank elevation before building the stand.

🏗️

Tank & Pipe Structural Design

Engineers use hydrostatic pressure to specify wall thickness, flange ratings, and valve pressure classes. Knowing the maximum head is the first step in any tank design.

🔧

Pump Selection

A pump must overcome both static head (height) and friction losses. This calculator gives you the static head component to feed into pump sizing calculations.

⛽

Fuel & Industrial Fluids

Diesel, oil, and other fluids have different densities. Pick the fluid or use the custom option to get pressure figures for non-water applications like fuel day tanks.

🏠

Rainwater Harvesting

Planning to gravity-feed from a raised rain barrel or tank? Measure from the water surface down to each outlet to see the pressure you'll get — before you build the stand. (An underground tank can't gravity-feed outlets above it; it needs a pump.)

🧮 Worked Example

Worked example: a 25 ft water column

A water tank sits on a tower so that its water surface is 25 ft (7.62 m) above a garden hose bib. What is the static pressure at the hose bib?

US units: 25 ft × 0.4335 psi/ft = 10.84 psi.
Metric: 1,000 kg/m³ × 9.80665 m/s² × 7.62 m = 74,727 Pa = 74.7 kPa, or 0.747 bar.
As head: 7.62 m, 25 ft or 300 in of water column.
Seawater in the same tank would give 10.84 × 1.025 = 11.11 psi.

That 10.8 psi is the reading with the tap shut. With water flowing, the pressure at the tap falls, because the pipe's friction uses some of the 25 ft — see the gravity feed flow rate calculator for how much flow that height can push through your pipe.

❓ FAQ

Frequently Asked Questions

How do I calculate water pressure from height?

Use the formula P = ρ × g × h. For fresh water in US units, pressure in psi equals height in feet × 0.433 — so a 20 ft column gives 8.67 psi. In metric, pressure in kPa equals height in metres × 9.81, so a 10 m 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?

It depends on the shower. Showers and mixer valves made for low-pressure gravity systems are commonly rated to work from about 0.1 bar (1.5 psi) — a 1 m (3.3 ft) head — although the flow is gentle at that level. Many standard valves and heads list a minimum of about 1 bar (14.5 psi, 10 m / 33 ft of head). In the US, plumbing codes size pipes to give at least 8 psi flowing at a shower, and WaterSense showerheads are tested down to 20 psi. A tank 3–5 m (10–16 ft) above the showerhead gives about 0.3–0.5 bar (4–7 psi), which is why a booster pump or a pumped ("power") shower 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 + about 14.7 psi (101.325 kPa) at sea level. 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. The US equivalent is feet of head: 1 ft = 0.433 psi, and 1 psi = 2.31 ft. Head is 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?

Only for points below the water surface in the tank — for example, the pressure on the tank floor or at an outlet lower than the water level. Most outlets are above an underground tank's water level, so water will not reach them by gravity at all; you need a pump. In that case, the height from the water surface up to the highest outlet is the static lift the pump must add (convert it with this calculator), and a surface pump can only draw water up by suction about 20–25 ft (6–7.5 m) in practice, so deep tanks need a submersible pump.

What PSI does a rooftop water tank typically produce?

A typical single-storey house has the rooftop tank 2–4 metres (7–13 ft) above its ground-floor taps, giving just 0.2–0.4 bar (about 3–6 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 / 14–21 psi) on the lower floors. US homes on a public supply usually see 40–80 psi, so many modern fixtures are designed for more than a low rooftop tank gives — hence the widespread use of pressure-boosting pumps.

✅ Sources & Review

Sources and review

The formula, constants and fixture figures on this page come from these references:

NIST Special Publication 811 — standard gravity (9.80665 m/s²) and the conversion factors for psi, bar, atm, mmHg and water column.
USGS Water Science School — Water Density: fresh water is about 1,000 kg/m³ (62.4 lb/ft³). NOAA — Sea Water: about 1,025 kg/m³.
University of Kentucky Cooperative Extension, HO-120: Ultra-low Pressure Drip Irrigation and Rainwater Catchment — drip tubing commonly run at 8–15 psi; ultra-low-pressure systems at 1–2 psi from tanks 2–5 ft up.
US EPA WaterSense — Showerheads: certified models are tested at 20, 45 and 80 psi. International Plumbing Code Table 604.3: 8 psi minimum flowing pressure for a shower.
Mira Showers (UK) — Low pressure gravity systems: typically a minimum cistern height of 1 m above the shower.

Reviewed by John Mac, PE, Water Systems Specialist

Texas-licensed Professional Engineer with 13+ years in residential water storage and 180+ tank projects. John writes and reviews every calculator on this site.

Last updated October 9, 2026

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