To convert pounds per square inch to inches of water, multiply by 27.67990582. That factor is the whole relationship: both units measure pressure, so the conversion is a proportion with no offset and no substance-specific constant.
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. Below the calculator there is a step table for the values people look up most, and a second table putting real pressure figures into inches of water so the number you get has something to be compared against.
The formula
pounds per square inch- The amount you are converting, in pounds per square inch
27.6799058214- The exact number of inches of water in one pound per square inch
inches of water- The converted result
How it works, step by step
- Enter the value in pounds per square inch.
- It is multiplied by 27.6799058214, the exact factor between the two units.
- The answer is shown in inches of water, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
A car tyre: 32 psi in inches of water
At 32 psi (a car tyre), the same quantity in inches of water is 32 × 27.6799 = 885.757 inH₂O. One pound per square inch is 27.6799 inches of water, so the numbers grow as expected.
A domestic water main: 58 psi in inches of water
At 58 psi (a domestic water main), the same quantity in inches of water is 58 × 27.6799 = 1605.43 inH₂O. One pound per square inch is 27.6799 inches of water, so the numbers grow as expected.
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Frequently asked questions
How many inches of water are in one pound per square inch?
Exactly 27.6799058214. 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 pounds per square inch to inches of water?
inches of water = pounds per square inch × 27.6799058214. Reversed, pounds per square inch = inches of water ÷ 27.6799058214, which is the same as multiplying by 0.0361272905497.
Which is the bigger unit, the pound per square inch or the inch of water?
The pound per square inch. One pound per square inch equals 27.6799 inches of water.
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 pound per square inch?
The dominant US pressure unit for tyres, plumbing and compressors.
What is a inch of water?
The low-pressure unit for duct static pressure and gas appliances in the US.
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 psi to inH₂O in my head?
Plenty of people do this in their head: multiply by 28 instead of using the exact factor 27.67990582. At 100 that shortcut gives 2800 inches of water, off by 32.01 inches of water or about 1.16%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Pounds Per Square Inch to inches of water reference tables
| Pounds Per Square Inch | Inches Of Water |
|---|---|
| 0.5 psi | 13.84 inH₂O |
| 1 psi | 27.6799 inH₂O |
| 2 psi | 55.3598 inH₂O |
| 3 psi | 83.0397 inH₂O |
| 5 psi | 138.4 inH₂O |
| 10 psi | 276.799 inH₂O |
| 20 psi | 553.598 inH₂O |
| 25 psi | 691.998 inH₂O |
| 50 psi | 1384 inH₂O |
| 75 psi | 2075.99 inH₂O |
| 100 psi | 2767.99 inH₂O |
| 250 psi | 6919.98 inH₂O |
| 500 psi | 13,840 inH₂O |
| 1000 psi | 27,679.9 inH₂O |
| 5000 psi | 138,400 inH₂O |
Exact factor: 1 pound per square inch = 27.6799058214 inches of water.
| Quantity | psi | inH₂O |
|---|---|---|
| Sea-level air | 14.7 psi | 406.8 inH₂O |
| A car tyre | 32 psi | 885.8 inH₂O |
| Blood pressure, systolic | 2.32 psi | 64.23 inH₂O |
| A bicycle tyre | 90 psi | 2491 inH₂O |
| A domestic water main | 58.02 psi | 1606 inH₂O |
| A steam boiler | 145 psi | 4015 inH₂O |
Published reference values, converted with the same factor this page uses.