Water pressure in psi = height of water in feet × 0.433. A 100 ft column of water pushes 43.3 psi at the bottom, and it takes 185 ft to reach 80 psi, the most static pressure the International Residential Code allows before a pressure reducing valve is required.
How head is converted to psi
Water weighs the same everywhere, so pressure depends only on the vertical height of the water above the point you measure, not on how wide the tank or pipe is.
pressure (psi) = head (ft) × 0.433
head (ft) = pressure (psi) ÷ 0.433, or psi × 2.31
IRC Appendix P computes static pressure change from height at 0.433 psi per foot, and the reciprocal is the familiar "1 psi lifts water 2.31 ft". In metric, 1 m of head is about 9.8 kPa. The calculator works in either direction: head to psi, psi to head, or the pressure at a fixture above or below a gauge.
Water pressure by height
| Height of water | Pressure |
|---|---|
| 10 ft | 4.3 psi |
| 20 ft | 8.7 psi |
| 30 ft | 13.0 psi |
| 46 ft | 19.9 psi |
| 50 ft | 21.7 psi |
| 100 ft | 43.3 psi |
| 150 ft | 65.0 psi |
| 185 ft | 80.1 psi |
Worked example: pressure at an upstairs fixture
Static pressure at a ground-floor gauge is 60 psi, and a second-floor shower is 20 ft higher. The height costs 20 × 0.433 = 8.66 psi, so the shower sees 60 − 8.66 = 51.3 psi with the water off. A basement tap 10 ft below the gauge gains 4.33 psi and sees 64.3 psi. Running water lowers both numbers by the friction loss in the pipe, which the calculator takes as an optional input.
The 80 psi limit
IRC P2903.3.1 requires a pressure reducing valve with a strainer on the water service pipe where static pressure exceeds 80 psi, set so the downstream pressure does not exceed 80 psi. The check under the answer compares your result with that limit. A pressure gauge on a hose bib shows your static pressure in a minute, and it is the number this calculator starts from.
Pressure from a tank or pump
A tank or tower supplies pressure by height alone: a 46 ft standpipe gives about 20 psi at the bottom. A private well adds a pump: for well pump sizing the pressure at the tank is converted to head at 2.31 ft per psi, so 50 psi is 115.5 ft and 60 psi is 138.6 ft. That head is added to the depth to the water when you size the pump, in the well pump size calculator.
The next questions
- Choosing a pump for a well? Use the well pump size calculator with your pressure.
- Running new supply lines? The PEX calculator totals the tubing, and the pipe slope calculator covers the drains.
- Hot water demand next? The tankless water heater size calculator and water softener size calculator both start from the household's fixtures.
- See every heating, cooling and plumbing calculator.