This page converts feet of water into pounds per square inch using the factor 0.4335275011, and shows the reverse figure alongside it. Both units measure pressure, which is why one number does the whole job.
The dominant US pressure unit for tyres, plumbing and compressors. Pump head expressed as a column of water — the way pump curves are drawn.
Gauge versus absolute. A tyre gauge reading 32 psi means 32 psi above atmospheric, which is about 46.7 psi absolute. Converting the number is straightforward; remembering which zero it was measured from is where the mistakes happen. N/mm² and MPa are the same size, so a drawing quoting either is quoting the same stress. The tables underneath give both a plain step-by-step lookup and a list of real quantities expressed in pounds per square inch, so you can sanity-check whether your answer is a plausible size.
The formula
feet of water- The amount you are converting, in feet of water
0.4335275011- The exact number of pounds per square inch in one foot of water
pounds per square inch- The converted result
How it works, step by step
- Enter the value in feet of water.
- It is multiplied by 0.4335275011, the exact factor between the two units.
- The answer is shown in pounds per square inch, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
Blood pressure, systolic: 5.35 ftH₂O in pounds per square inch
At 5.35 ftH₂O (blood pressure, systolic), the same quantity in pounds per square inch is 5.35 × 0.433528 = 2.31937 psi. One foot of water is 0.433528 pounds per square inch, so the numbers shrink as expected.
A bicycle tyre: 208 ftH₂O in pounds per square inch
A bicycle tyre comes to about 208 ftH₂O. Multiplying by the factor: 208 × 0.433528 = 90.1737 psi. Dividing the answer back by 0.433528 returns the figure you started with, which is the quickest way to check you have the factor the right way up.
How to read your score
Frequently asked questions
How many pounds per square inch are in one foot of water?
Exactly 0.4335275011. Every figure on this page is that one number multiplied by your input, so the only rounding is at the display step.
What is the formula to convert feet of water to pounds per square inch?
pounds per square inch = feet of water × 0.4335275011. Reversed, feet of water = pounds per square inch ÷ 0.4335275011, which is the same as multiplying by 2.30665874128.
Which is the bigger unit, the foot of water or the pound per square inch?
The pound per square inch. One foot of water is only 0.433528 of a pound per square inch, so it takes 2.30666 feet of water to make one pound per square inch.
What does this quantity actually measure?
Both units measure pressure. That is why a single factor is enough: there is no temperature offset and no material property involved, unlike conversions that cross between different quantities.
What is a foot of water?
Pump head expressed as a column of water — the way pump curves are drawn.
What is a pound per square inch?
The dominant US pressure unit for tyres, plumbing and compressors.
Why does my answer differ from another converter?
Almost always because the other tool rounded the factor before multiplying. This page keeps full double precision through the calculation and rounds only for display, and it prints the factor it used so you can see where any difference came from.
Is there a quick way to do ftH₂O to psi in my head?
Plenty of people do this in their head: divide by 2.3 instead of using the exact factor 0.4335275011. At 100 that shortcut gives 43.478261 pounds per square inch, off by 0.1255 pounds per square inch or about 0.29%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Feet Of Water to pounds per square inch reference tables
| Feet Of Water | Pounds Per Square Inch |
|---|---|
| 0.5 ftH₂O | 0.216764 psi |
| 1 ftH₂O | 0.433528 psi |
| 2 ftH₂O | 0.867055 psi |
| 3 ftH₂O | 1.30058 psi |
| 5 ftH₂O | 2.16764 psi |
| 10 ftH₂O | 4.33528 psi |
| 20 ftH₂O | 8.67055 psi |
| 25 ftH₂O | 10.8382 psi |
| 50 ftH₂O | 21.6764 psi |
| 75 ftH₂O | 32.5146 psi |
| 100 ftH₂O | 43.3528 psi |
| 250 ftH₂O | 108.382 psi |
| 500 ftH₂O | 216.764 psi |
| 1000 ftH₂O | 433.528 psi |
| 5000 ftH₂O | 2167.64 psi |
Exact factor: 1 foot of water = 0.4335275011 pounds per square inch.
| Quantity | ftH₂O | psi |
|---|---|---|
| Sea-level air | 33.9 ftH₂O | 14.7 psi |
| A car tyre | 73.81 ftH₂O | 32 psi |
| Blood pressure, systolic | 5.352 ftH₂O | 2.32 psi |
| A bicycle tyre | 207.6 ftH₂O | 90 psi |
| A domestic water main | 133.8 ftH₂O | 58.02 psi |
| A steam boiler | 334.6 ftH₂O | 145 psi |
Published reference values, converted with the same factor this page uses.