In short: every foot a water source sits above a fixture adds about 0.433 psi of static pressure (roughly 2.31 ft per psi). A rooftop tank 25 ft up produces about 10.8 psi on its own — add whatever pressure is already in the line, from a pump or utility main, to get the total your fixture will actually see.
These figures are planning aids based on standard hydrostatics. For code compliance, pressure-reducing-valve sizing or other safety-critical work, confirm with a licensed engineer or your water utility.
How to calculate water pressure from height
Water pressure from elevation comes from the weight of the water column above the point you're measuring. The taller the column, the more weight is pressing down, and the higher the pressure. If the source is also pressurized — by a pump or a utility main — that pressure simply adds on top.
Worked example. Take the calculator's default settings: a source 25 ft above the point, fresh water at 20 °C, no added source pressure. Convert height to meters: 25 × 0.3048 = 7.62 m. Water at 20 °C has a density of about 998.2 kg/m³. Multiply: 998.2 × 9.80665 × 7.62 ≈ 74,600 pascals. Divide by 6,894.76 pascals per psi to get about 10.8 psi — the same figure the tool shows above. For a quick mental shortcut without the full calculation, the PSI calculator handles plain unit conversions once you already have a pressure figure.
Path doesn't matter, only net height does. Whether the pipe runs straight down or winds through the building, Pascal's principle means only the net vertical drop between source and point sets the static pressure. Horizontal runs, bends and loops don't add or subtract elevation pressure — though they do add friction losses once water is flowing, which this calculator doesn't model.
Why height — and temperature — change the answer
Height dominates the answer because it sets how much water is stacked above the point in question; that entire column's weight is what creates the pressure. Temperature plays a much smaller, secondary role: warmer water is less dense, so a given height of hot water weighs slightly less and produces slightly less pressure than the same height of cold water. This calculator uses the Kell equation, the standard reference for water density from 0 °C to 150 °C, so the effect is captured automatically rather than assumed away. You can read the full method on our methodology page.
Salinity works the same way in the other direction: seawater is denser than fresh water, so the same height of seawater produces slightly more pressure — about 2–3% more at typical ocean salinity.
Water pressure by height
Static gauge pressure produced by fresh water at 20 °C alone, with no added source pressure. Values are rounded to 3 significant figures; the calculator above gives the exact figure for your inputs.
| Height | psi | bar | kPa |
|---|---|---|---|
| 1 ft / 0.30 m | 0.433 | 0.0299 | 2.98 |
| 5 ft / 1.52 m | 2.16 | 0.149 | 14.9 |
| 10 ft / 3.05 m | 4.33 | 0.298 | 29.8 |
| 20 ft / 6.10 m | 8.65 | 0.597 | 59.7 |
| 25 ft / 7.62 m (default) | 10.8 | 0.746 | 74.6 |
| 33 ft / 10.1 m | 14.3 | 0.985 | 98.5 |
| 50 ft / 15.2 m | 21.6 | 1.49 | 149 |
| 75 ft / 22.9 m | 32.5 | 2.24 | 224 |
| 100 ft / 30.5 m | 43.3 | 2.98 | 298 |
Worked examples
Rooftop tank, 25 ft above the kitchen tap
10.8 psi
A gravity-fed rooftop tank with no pump, sitting 25 ft above the faucet, delivers about 10.8 psi on its own — on the low end for comfortable fixture flow, which is why most tank-fed buildings add a booster pump.
Two-story home, tank 20 ft up
8.65 psi
Slightly less height means slightly less pressure: about 8.65 psi, following the same 0.433 psi-per-foot relationship.
Booster pump feeding a fixture 8 ft above the meter
≈ 41.5 psi
A pump or utility main supplying 45 psi at the meter, feeding a fixture 8 ft higher, loses about 3.46 psi to that extra lift — leaving roughly 41.5 psi at the fixture. Enter -8 ft as the height and 45 psi as the source pressure to see this.
What else affects the result
Flow, not just static pressure. This calculator gives the static (no-flow) pressure at a point. Once water is actually moving, friction inside the pipe reduces the pressure further — more so in long, narrow or rough pipes. For that, see the friction loss calculator or the Hazen–Williams calculator.
Fittings and valves. Elbows, tees and partly closed valves each cost a little pressure once water flows through them, on top of straight-pipe friction.
Dissolved salts. Brine, pool water or seawater are denser than fresh water, so switch the water type above (or enter a custom density) if you're not working with plain fresh water.
Compressibility. Water is nearly incompressible, so — outside deep-ocean or industrial high-pressure settings — pressure itself doesn't meaningfully change water's density. Only temperature and salinity do.
Frequently asked questions
What is normal water pressure for a house?
Most plumbing codes, including the International Plumbing Code, treat 40–80 psi of static pressure as the normal working range for a home. Below about 40 psi, fixtures and upper floors can feel weak. Above 80 psi, code generally requires a pressure-reducing valve to protect pipes, valves and appliances from premature failure.
How do you calculate water pressure from height?
Multiply the density of water by gravity and by the height of the water source above the point you care about: P = ρ × g × h. As a shortcut for cold water, every foot of elevation adds about 0.433 psi, or every 2.31 feet adds about 1 psi. This calculator uses the exact temperature-adjusted density instead of the rounded shortcut.
Does water temperature affect pressure?
Yes, slightly, because warmer water is less dense. The effect is small for normal indoor temperatures but grows toward boiling: water at 100 °C is roughly 4% less dense than water at its coldest, so a given height produces about 4% less pressure at that temperature.
What if my water source is below the fixture?
Enter a negative height. Gravity then works against you: the fixture sits above the source, so elevation alone cannot deliver positive pressure there. You need a pump or pressurized supply to lift water to that point, which is why this calculator lets you add a source pressure on top of the height.
How much water pressure do I lose per floor?
A typical residential story is about 10 feet floor-to-floor, which costs roughly 4.3 psi of static pressure per floor climbed. For a full floor-by-floor breakdown of a multi-story building, use the dedicated water pressure by floor calculator.
How is this different from the water pressure at depth calculator?
Both use the same hydrostatic formula, but for different situations. This calculator finds the pressure delivered to a plumbing fixture by a source that sits above it, such as a tank, tower or attic cistern. The water pressure at depth calculator instead finds the pressure acting on something submerged below a water surface, such as a diver, pool wall or the bottom of a tank.
Sources & references
- Pascal, B. (1663). Treatise on the Equilibrium of Liquids and on the Weight of the Mass of Air.
- International Code Council. International Plumbing Code (IPC), Section 604 — Design of Building Water Distribution System.
- 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.
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)