Plumbing
Water Pressure Calculator
Work out pressure at a point after elevation and friction losses, or what static pressure a height requires.
Result
Pipe and drain sizing is governed by plumbing code (IPC/UPC or local equivalent) and must be designed and installed by a licensed plumber. This is an educational estimate, not a design. Static pressure should be measured at a hose bib with no flow. Dynamic pressure during flow is always lower.
Get a Free Business AuditWhat moves the number
- Elevation, which costs roughly 0.433 psi per foot of rise.
- Friction loss through the run at the design flow.
- Whether the reading is static or flowing, which differ substantially.
Where this one goes wrong
Diagnosing from static pressure alone. A system can read healthy with nothing running and collapse under flow, and the flowing reading is the one that matches what the customer experiences.
Before you quote
- Static and flowing pressure both, at the same point.
- Whether a pressure reducing valve is present and what it is set to.
- Whether pressure is too high, which damages fixtures and appliances.
Questions
About this calculator
Static or flowing pressure, which matters?
Both, and the gap between them is the diagnosis. A large drop under flow points at a restriction; a low static reading points at the supply or a reducing valve.
How much pressure does height cost?
About 0.433 psi per foot. A third floor fixture starts well down on whatever arrives at the meter before any friction is counted.
Can pressure be too high?
Yes. Excessive pressure stresses fixtures, appliances and joints and shortens their life. Where it is high, a pressure reducing valve is usually the right answer rather than living with it.
The formula
1 PSI = 2.31 feet of head; elevation loss (PSI) = height × 0.433
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How to use this calculator
- Supply pressure (PSI). Enter your own figure; the page starts at 60.
- Height above the supply (ft). Enter your own figure; the page starts at 20.
- Friction loss in the run (PSI). Enter your own figure; the page starts at 6.
- Pressure the fixture needs (PSI). Enter your own figure; the page starts at 20.
The result updates as you type, so you can try a figure, see what it does to pressure at the fixture, and change it back. Nothing you enter is sent anywhere or saved.
A worked example
These are the figures the calculator opens with. Every number in the results column below is produced by the same calculation the page runs, so you can follow it through before putting your own figures in.
What goes in
| Input | Value |
|---|---|
| Supply pressure (PSI) | 60 |
| Height above the supply (ft) | 20 |
| Friction loss in the run (PSI) | 6 |
| Pressure the fixture needs (PSI) | 20 |
What comes out
| Result | Value |
|---|---|
| Pressure at the fixture main result | 45.3 |
| Loss from elevation | 8.7 |
| Supply pressure as head | 138.6 |
| Margin above the fixture requirement | 25.3 |
Pressure at the fixture is 45.3 PSI. 25.3 PSI above what it needs.
How sensitive the answer is
Holding everything else steady and changing only supply pressure (psi), this is what happens to pressure at the fixture. It is worth knowing which of your inputs the answer actually hinges on, and which barely move it.
| Supply pressure (PSI) | Pressure at the fixture |
|---|---|
| 30 | 15.3 |
| 45 | 30.3 |
| 60 example above | 45.3 |
| 90 | 75.3 |
| 120 | 105.3 |
Every other input is held at the example value while this one changes, which is not how a real job behaves. Treat it as a guide to which number matters most, not as five separate quotes.
What each figure means
- Supply pressure (PSI)
- A number, between 0 and 500, starting at 60.
- Height above the supply (ft)
- A number, between 0 and 2000, starting at 20.
- Friction loss in the run (PSI)
- A number, between 0 and 200, starting at 6.
- Pressure the fixture needs (PSI)
- A number, between 0 and 200, starting at 20.
What the results tell you
| Result | What it is |
|---|---|
| Pressure at the fixture | The headline result. A decimal figure. |
| Loss from elevation | A decimal figure. |
| Supply pressure as head | A decimal figure. |
| Margin above the fixture requirement | A decimal figure. |
Before you rely on this number
Pipe sizing, flow and pressure figures depend on the actual fittings, the run, the material and local code. Code requirements vary by jurisdiction and override any general calculation, so check what applies where the work is happening.
Keep going
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