To convert feet of water to kilopounds per square inch, multiply by 0.0004335275011. That factor is the whole relationship: both units measure pressure, so the conversion is a proportion with no offset and no substance-specific constant.
Pump head expressed as a column of water — the way pump curves are drawn. One thousand psi; the unit US steel and alloy strengths are quoted in.
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 kilopounds 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
0.0004335275011- The exact number of kilopounds per square inch in one foot of water
kilopounds per square inch- The converted result
How it works, step by step
- Enter the value in feet of water.
- It is multiplied by 0.0004335275011, the exact factor between the two units.
- The answer is shown in kilopounds 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 kilopounds per square inch
Take blood pressure, systolic, roughly 5.35 ftH₂O. The conversion is a single multiplication — 5.35 × 0.000433528 — giving 0.00231937 ksi. Because the relationship is proportional, doubling the input doubles the answer to 0.00463874 ksi.
Sea-level air: 33.9 ftH₂O in kilopounds per square inch
Sea-level air comes to about 33.9 ftH₂O. Multiplying by the factor: 33.9 × 0.000433528 = 0.0146966 ksi. Dividing the answer back by 0.000433528 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 kilopounds per square inch are in one foot of water?
Exactly 0.0004335275011. 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 kilopounds per square inch?
kilopounds per square inch = feet of water × 0.0004335275011. Reversed, feet of water = kilopounds per square inch ÷ 0.0004335275011, which is the same as multiplying by 2306.65874128.
Which is the bigger unit, the foot of water or the kilopound per square inch?
The kilopound per square inch. One foot of water is only 0.000433528 of a kilopound per square inch, so it takes 2306.66 feet of water to make one kilopound 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 kilopound per square inch?
One thousand psi; the unit US steel and alloy strengths are quoted in.
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 ksi in my head?
Plenty of people do this in their head: divide by 2300 instead of using the exact factor 0.0004335275011. At 100 that shortcut gives 0.043478261 kilopounds per square inch, off by 0.0001255 kilopounds 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 kilopounds per square inch reference tables
| Feet Of Water | Kilopounds Per Square Inch |
|---|---|
| 0.5 ftH₂O | 0.000216764 ksi |
| 1 ftH₂O | 0.000433528 ksi |
| 2 ftH₂O | 0.000867055 ksi |
| 3 ftH₂O | 0.00130058 ksi |
| 5 ftH₂O | 0.00216764 ksi |
| 10 ftH₂O | 0.00433528 ksi |
| 20 ftH₂O | 0.00867055 ksi |
| 25 ftH₂O | 0.0108382 ksi |
| 50 ftH₂O | 0.0216764 ksi |
| 75 ftH₂O | 0.0325146 ksi |
| 100 ftH₂O | 0.0433528 ksi |
| 250 ftH₂O | 0.108382 ksi |
| 500 ftH₂O | 0.216764 ksi |
| 1000 ftH₂O | 0.433528 ksi |
| 5000 ftH₂O | 2.16764 ksi |
Exact factor: 1 foot of water = 0.0004335275011 kilopounds per square inch.
| Quantity | ftH₂O | ksi |
|---|---|---|
| Sea-level air | 33.9 ftH₂O | 0.0147 ksi |
| A car tyre | 73.81 ftH₂O | 0.032 ksi |
| Blood pressure, systolic | 5.352 ftH₂O | 0.00232 ksi |
| A bicycle tyre | 207.6 ftH₂O | 0.09 ksi |
| A domestic water main | 133.8 ftH₂O | 0.05802 ksi |
| A steam boiler | 334.6 ftH₂O | 0.145 ksi |
Published reference values, converted with the same factor this page uses.