In short: pressure from a water column follows P = ρgh — 10 ft of fresh water at room temperature produces about 4.33 psi (29.8 kPa) of gauge pressure. The common field rule of thumb is 0.433 psi per foot of head (or divide feet by 2.31). Use the calculator above for any height, water type and temperature.
These figures are planning aids based on standard hydrostatic and thermophysical data. For system design or code compliance, confirm with a licensed engineer.
How to convert head to pressure
"Head" is simply the height of a column of water above the point you care about. Because water has weight, a taller column pushes down harder — and that push is pressure. The relationship is the hydrostatic pressure equation, one of the most-used formulas in plumbing and water-system engineering:
This calculator converts your head to meters, looks up (or accepts) a water density, multiplies by gravity, and converts the pascal result into the pressure units you actually work with. For the reverse conversion — a known pressure back to a head — use the pressure to head calculator instead; for a plain unit conversion of a pressure you already have, use the psi calculator.
Worked example. Take 10 ft of fresh water at 20 °C. Convert to meters: 10 × 0.3048 = 3.048 m. Water at 20 °C has a density of 998.2 kg/m³. Multiply: 998.2 × 9.80665 × 3.048 ≈ 29,837 Pa, which is 29.84 kPa or 4.327 psi — exactly what the calculator shows with its default values.
Gauge vs. absolute, in one line. Gauge pressure (the default here) is pressure above the surrounding atmosphere — what a pressure gauge actually reads and what plumbing and pump specs almost always mean. Absolute pressure adds standard atmospheric pressure (101.325 kPa, 14.696 psi) on top, and matters mainly in vacuum, gas-law or scientific contexts.
Pressure by head (fresh water, 20 °C, gauge)
The values this calculator computes across a range of heights. Because the relationship is linear, doubling the head exactly doubles the pressure.
| Head | psi | kPa | bar |
|---|---|---|---|
| 1 ft | 0.433 | 2.984 | 0.0298 |
| 2 ft | 0.865 | 5.967 | 0.0597 |
| 5 ft | 2.164 | 14.918 | 0.1492 |
| 10 ft (default) | 4.327 | 29.837 | 0.2984 |
| 20 ft | 8.655 | 59.674 | 0.5967 |
| 30 ft | 12.983 | 89.511 | 0.8951 |
| 50 ft | 21.637 | 149.185 | 1.4918 |
| 100 ft | 43.275 | 298.370 | 2.9837 |
Pressure in every unit, at three common heights
The same fresh-water, 20 °C, gauge-pressure result shown across all five units this calculator reports.
| Head | psi | kPa | bar | atm | kg/cm² |
|---|---|---|---|---|---|
| 10 ft | 4.327 | 29.837 | 0.2984 | 0.2945 | 0.3043 |
| 20 ft | 8.655 | 59.674 | 0.5967 | 0.5889 | 0.6085 |
| 50 ft | 21.637 | 149.185 | 1.4918 | 1.4723 | 1.5213 |
Worked examples
Elevated tank, 10 ft above the tap
4.33 psi
A tank with its water surface 10 ft above a fixture delivers about 4.33 psi of static pressure at that fixture — often too low for good flow, which is why most homes rely on a pump or municipal supply pressure instead.
Water tower standpipe, 100 ft
43.28 psi
A 100 ft elevated standpipe — typical for a small-town water tower — produces about 43.28 psi of gauge pressure at ground level, comfortably in the normal municipal supply range.
Same 10 ft column, seawater
4.44 psi
Switch the water type to seawater and the same 10 ft column produces about 4.44 psi — roughly 2.6% more than fresh water, from salt's added density.
What else affects the result
Water temperature. Warmer water is less dense, so a fixed height of hot water exerts slightly less pressure than the same height of cold water — the difference is about 4% between freezing and boiling, but under half a percent across ordinary indoor temperatures. It matters more for hot process water than for everyday plumbing.
Dissolved salts. Seawater and brine are denser than fresh water, so the same head produces more pressure — use the seawater preset or a custom density for pool, well or industrial fluids that aren't plain fresh water.
Local atmospheric pressure. This calculator's absolute-pressure option adds the standard sea-level value (101.325 kPa). Actual atmospheric pressure varies with elevation and weather, so at altitude, or in very precise scientific work, the true absolute pressure will differ slightly from what's shown.
Frequently asked questions
What is the formula to convert head to pressure?
Pressure equals P = ρ × g × h, where ρ is water density, g is gravitational acceleration (9.80665 m/s²) and h is the head — the vertical height of the water column. Multiply density by gravity by height and you get pressure in pascals, which this calculator also converts to psi, kPa, bar, atm and kg/cm².
How many psi is 1 foot of water head?
About 0.433 psi per foot of head, using the common rule of thumb (also written as the "2.31 rule": divide head in feet by 2.31 to get psi). This calculator computes it precisely for your exact water temperature — at 20 °C it works out to 0.4327 psi per foot.
Gauge or absolute pressure — which should I use?
Gauge pressure — the default — is what plumbing, pump and irrigation work almost always means: pressure above normal atmospheric pressure, which is what a pressure gauge reads. Absolute pressure adds standard atmospheric pressure (101.325 kPa, 14.696 psi) on top, and is used mainly in scientific, vacuum or gas-law contexts.
Does water temperature change the pressure from a given head?
Slightly. Warmer water is less dense, so a fixed height of hot water exerts a bit less pressure than the same height of cold water — around 4% less at boiling versus freezing. Across ordinary indoor temperatures (10–30 °C) the difference is under half a percent, small enough to ignore for most plumbing work but worth including for hot process water.
How is this different from a general PSI converter?
A plain unit converter only rescales a pressure value you already have. This calculator derives the pressure itself from a physical water column height and density using P = ρgh — you enter a height, not a pressure. For converting an existing pressure value between units, use the psi calculator instead.
What about seawater or other liquids?
Switch the water type to seawater, which adds roughly 2.65% to fresh water's density at typical ocean salinity, or choose custom density to enter the exact density of another liquid — brine, a chemical solution or anything else you're working with.
Sources & references
- Kell, G. S. (1975). Density, thermal expansivity, and compressibility of liquid water from 0° to 150 °C. Journal of Chemical & Engineering Data, 20(1), 97–105.
- National Institute of Standards and Technology (NIST). Thermophysical Properties of Fluid Systems.
- U.S. Standard Atmosphere (1976) — reference sea-level atmospheric pressure (101.325 kPa) used for the absolute-pressure option.
John Mac, PE
Water Systems Specialist · Austin, Texas
Texas-licensed Professional Engineer with 13+ years in residential water systems and 180+ completed projects. Writes and reviews the calculators on watercalculator.us. Read full bio
Texas PE (2016) · BS Civil Engineering, Hydraulics (2013)