In short: static water pressure comes from height alone. Every foot of standing fresh water adds about 0.433 psi (2.98 kPa), so a 10 ft tank produces roughly 4.33 psi at its base with the tap closed. Once water starts flowing, friction lowers the reading below this static value — use the calculator above for any height, water type or temperature.
These figures are planning aids based on standard hydrostatics. For plumbing code compliance or structural work, confirm with a licensed engineer or your local inspector.
How to calculate static pressure
Static pressure is the simplest kind of water pressure to calculate, because it depends on only one thing: the height of standing water above the point you're measuring. There is no flow, so there is no friction to account for — just the weight of the water column pressing down.
This calculator converts your height to meters, looks up the density of water at the temperature and water type you selected, and multiplies by standard gravity to get pressure in pascals — then converts that into every common pressure unit. A common shortcut for fresh water at room temperature: every foot of height adds about 0.433 psi, and every meter adds about 9.79 kPa.
Worked example. A rooftop tank sits 10 ft above a ground-floor tap. Ten feet is 3.048 m. Fresh 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 4.33 psi. That single multiplication — then a unit conversion — is all the calculator is doing.
Static vs. dynamic pressure, in one line. Static pressure is what a gauge reads with the tap closed and nothing flowing. Dynamic (working) pressure is what it reads once water is moving, and it's always lower because friction inside the pipe eats into the static value. For pressure while flowing through a specific pipe run, see the Total Dynamic Head Calculator.
Why height — not flow — sets static pressure
Static pressure at any point in a standing column of water depends only on the vertical distance between that point and the water's free surface above it. It does not depend on the shape of the tank or pipe, how much water is stored in total, or the diameter of the pipe — only on height. A narrow standpipe and a wide water tower at the same elevation produce identical static pressure at their base.
Temperature and water type make a smaller, secondary difference by changing density. Warmer water is slightly less dense, so a given height of hot water exerts a touch less pressure than the same height of cold water — under 4% between 4 °C and 100 °C. Seawater and brine are denser than fresh water, so the same height produces more pressure. This calculator uses the Kell equation, the reference-standard fit for the density of water, so these small differences are captured accurately. You can read the full method on our methodology page.
Static pressure by column height
Fresh water at 20 °C (68 °F), gauge pressure. Use this table for a quick lookup, or the calculator above for other temperatures, water types or absolute pressure.
| Height | psi | kPa |
|---|---|---|
| 1 ft | 0.4327 | 2.984 |
| 5 ft | 2.164 | 14.918 |
| 10 ft | 4.327 | 29.837 |
| 20 ft | 8.655 | 59.674 |
| 30 ft | 12.982 | 89.511 |
| 50 ft | 21.637 | 149.2 |
| 100 ft | 43.275 | 298.4 |
| 150 ft | 64.912 | 447.6 |
| 200 ft | 86.55 | 596.7 |
Worked examples
Rooftop tank feeding a ground tap
4.33 psi
A gravity-fed rooftop tank 10 ft above a ground-floor tap produces about 4.33 psi (29.8 kPa) static pressure with the tap closed — well below the roughly 40–60 psi most fixtures expect, which is why elevated tanks alone often aren't enough.
Water tower supplying a subdivision
43.3 psi
A water tower with 100 ft of elevation above street level delivers about 43.3 psi (298.4 kPa) of static pressure — a typical target range for municipal distribution systems.
Bottom of a 300 ft well casing
129.8 psi
Static water pressure at the base of a 300 ft column — such as the standing water level in a deep well — reaches about 129.8 psi (895.1 kPa), which is why submersible well pumps must be rated well beyond typical household pressures.
What else affects the reading
Dissolved salts. Seawater is about 2–3% denser than fresh water, so the same height of seawater or brine produces slightly more static pressure — roughly 1,025 kg/m³ versus 998. Use the water-type selector or a custom density for pool, brine or seawater work.
Gauge vs. absolute. Ordinary pressure gauges read gauge pressure, treating the surrounding atmosphere as zero. Absolute pressure adds roughly 14.7 psi (101.3 kPa) of atmospheric pressure at sea level on top of that. Use the advanced toggle if you need the absolute figure.
Flow and friction. The moment water starts moving, friction inside the pipe — from length, diameter, roughness and fittings — reduces the pressure below the static value calculated here. For pressure while water is flowing through a real pipe run, see the Friction Loss Calculator or the Total Dynamic Head Calculator.
Frequently asked questions
What is static pressure in a water system?
Static pressure is the pressure in a water system when no water is flowing — for example, a closed tap. It comes entirely from the height of water above the measuring point (elevation head). Once water starts flowing, friction in the pipe lowers the reading to the dynamic, or working, pressure.
How do I calculate static water pressure from tank height?
Multiply the height of the water column by the density of water and by gravity: P = ρ·g·h. As a shortcut for fresh water, every foot of height adds about 0.433 psi (2.98 kPa), so a 10 ft tank produces roughly 4.33 psi at its base.
Does water temperature affect static pressure?
Slightly. Warmer water is less dense, so a given height of hot water exerts a little less pressure than the same height of cold water. The difference is under 4% between 4 °C and 100 °C, which is negligible for most household and building work but included here for accuracy.
What is the difference between static and dynamic pressure?
Static pressure is measured with no flow and depends only on height. Dynamic (working) pressure is measured while water is flowing and is always lower, because friction inside the pipe consumes some of the available pressure. The gap between the two grows with higher flow rates and longer, narrower, or rougher pipe runs.
Is a pressure gauge reading gauge or absolute pressure?
Ordinary plumbing and household pressure gauges read gauge pressure, which treats normal atmospheric pressure as the zero point. Absolute pressure adds atmospheric pressure (about 14.7 psi / 101.3 kPa at sea level) on top of that gauge reading.
Sources & references
- Çengel, Y. A., & Cimbala, J. M. (2020). Fluid Mechanics: Fundamentals and Applications. McGraw-Hill.
- National Institute of Standards and Technology (NIST). Standard gravity and SI unit definitions.
- American Water Works Association (AWWA). M22 — Sizing Water Service Lines and Meters.
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)