One inch of water is exactly 0.03612729055 pounds per square inch, so converting inches of water to pounds per square inch is a single multiplication. Enter any figure and the result appears as you type — the arithmetic runs in your browser, so nothing is sent anywhere.
The dominant US pressure unit for tyres, plumbing and compressors. The low-pressure unit for duct static pressure and gas appliances in the US.
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
inches of water- The amount you are converting, in inches of water
0.0361272905497- The exact number of pounds per square inch in one inch of water
pounds per square inch- The converted result
How it works, step by step
- Enter the value in inches of water.
- It is multiplied by 0.0361272905497, 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
Sea-level air: 407 inH₂O in pounds per square inch
Sea-level air comes to about 407 inH₂O. Multiplying by the factor: 407 × 0.0361273 = 14.7038 psi. Dividing the answer back by 0.0361273 returns the figure you started with, which is the quickest way to check you have the factor the right way up.
Blood pressure, systolic: 64.2 inH₂O in pounds per square inch
At 64.2 inH₂O (blood pressure, systolic), the same quantity in pounds per square inch is 64.2 × 0.0361273 = 2.31937 psi. One inch of water is 0.0361273 pounds per square inch, so the numbers shrink as expected.
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Frequently asked questions
How many pounds per square inch are in one inch of water?
Exactly 0.0361272905497. 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 inches of water to pounds per square inch?
pounds per square inch = inches of water × 0.0361272905497. Reversed, inches of water = pounds per square inch ÷ 0.0361272905497, which is the same as multiplying by 27.6799058214.
Which is the bigger unit, the inch of water or the pound per square inch?
The pound per square inch. One inch of water is only 0.0361273 of a pound per square inch, so it takes 27.6799 inches 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 inch of water?
The low-pressure unit for duct static pressure and gas appliances in the US.
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 inH₂O to psi in my head?
Plenty of people do this in their head: divide by 28 instead of using the exact factor 0.03612729055. At 100 that shortcut gives 3.5714286 pounds per square inch, off by 0.0413 pounds per square inch or about 1.14%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Inches Of Water to pounds per square inch reference tables
| Inches Of Water | Pounds Per Square Inch |
|---|---|
| 0.5 inH₂O | 0.0180636 psi |
| 1 inH₂O | 0.0361273 psi |
| 2 inH₂O | 0.0722546 psi |
| 3 inH₂O | 0.108382 psi |
| 5 inH₂O | 0.180636 psi |
| 10 inH₂O | 0.361273 psi |
| 20 inH₂O | 0.722546 psi |
| 25 inH₂O | 0.903182 psi |
| 50 inH₂O | 1.80636 psi |
| 75 inH₂O | 2.70955 psi |
| 100 inH₂O | 3.61273 psi |
| 250 inH₂O | 9.03182 psi |
| 500 inH₂O | 18.0636 psi |
| 1000 inH₂O | 36.1273 psi |
| 5000 inH₂O | 180.636 psi |
Exact factor: 1 inch of water = 0.0361272905497 pounds per square inch.
| Quantity | inH₂O | psi |
|---|---|---|
| Sea-level air | 406.8 inH₂O | 14.7 psi |
| A car tyre | 885.8 inH₂O | 32 psi |
| Blood pressure, systolic | 64.23 inH₂O | 2.32 psi |
| A bicycle tyre | 2491 inH₂O | 90 psi |
| A domestic water main | 1606 inH₂O | 58.02 psi |
| A steam boiler | 4015 inH₂O | 145 psi |
Published reference values, converted with the same factor this page uses.