Plumbing
Plumbing Water Pressure Calculator
Check pressure at a fixture against what the supply provides once height and pipe run are accounted for.
Result
Static pressure only. This is the pressure with nothing flowing; once water moves, friction in the pipe and through fittings takes more, and that loss grows with the square of the flow.
Get a Free Business AuditWhat moves the number
- Height above the supply point.
- Friction through the developed length at the flow being drawn.
- Any reducing valve, filter or softener in the path.
Where this one goes wrong
Replacing pipe to fix a pressure complaint caused by a reducing valve. The valve is a five minute check and is frequently the answer, and a repipe that does not address it changes nothing.
Questions
About this calculator
What should I check first on a low pressure call?
The main shutoff and any pressure reducing valve, both of which are quick and both of which are common causes. Opening the walls before checking them is expensive.
Why is pressure worse upstairs?
Elevation. Every foot of rise costs pressure, so upper floors always start lower, and a marginal supply shows there first.
Does a filter reduce pressure?
A loaded one does, sometimes severely. Whole-house filters are a frequent cause of a gradual pressure complaint and are worth checking before anything else is suspected.
The formula
pressure lost to height = feet x 0.433 PSI
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How to use this calculator
- Work out. Enter your own figure; the page starts at Pressure at the bottom from a height.
- 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 25.
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 |
|---|---|
| Work out | Pressure at the bottom from a height |
| Supply pressure (PSI) | 60 |
| Height above the supply (ft) | 25 |
What comes out
| Result | Value |
|---|---|
| Pressure at the fixture main result | 49.2 |
| Lost to height | 10.8 |
| That pressure as head | 0.0 |
| Supply pressure | 4.1 |
Lifting water 25 feet costs 10.8 PSI, so 49.2 PSI arrives at the fixture. 49.2 PSI is equivalent to 0.0 feet of head.
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 | 19.2 |
| 45 | 34.2 |
| 60 example above | 49.2 |
| 90 | 79.2 |
| 120 | 109.2 |
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
- Work out
- Choose from Pressure at the bottom from a height, Height from a pressure.
- Supply pressure (PSI)
- A number, between 0 and 300, starting at 60.
- Height above the supply (ft)
- A number, between 0 and 1000, starting at 25.
What the results tell you
| Result | What it is |
|---|---|
| Pressure at the fixture | The headline result. A decimal figure. |
| Lost to height | A decimal figure. |
| That pressure as head | A decimal figure. |
| Supply pressure | 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.
Estimating is the easy part
The jobs you never hear about cost more than the ones you mis-measure. BDEVY builds the marketing, systems and automation that bring them in.