To convert inches of water to pascals, multiply by 249.0889. 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 SI unit: one newton per square metre. 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 pascals, 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
249.0889- The exact number of pascals in one inch of water
pascals- The converted result
How it works, step by step
- Enter the value in inches of water.
- It is multiplied by 249.0889, the exact factor between the two units.
- The answer is shown in pascals, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
A domestic water main: 1610 inH₂O in pascals
A domestic water main comes to about 1610 inH₂O. Multiplying by the factor: 1610 × 249.089 = 401,033 Pa. Dividing the answer back by 249.089 returns the figure you started with, which is the quickest way to check you have the factor the right way up.
A steam boiler: 4010 inH₂O in pascals
At 4010 inH₂O (a steam boiler), the same quantity in pascals is 4010 × 249.089 = 998,846 Pa. One inch of water is 249.089 pascals, so the numbers grow as expected.
How to read your score
Frequently asked questions
How many pascals are in one inch of water?
Exactly 249.0889. 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 pascals?
pascals = inches of water × 249.0889. Reversed, inches of water = pascals ÷ 249.0889, which is the same as multiplying by 0.00401463092093.
Which is the bigger unit, the inch of water or the pascal?
The inch of water. One inch of water equals 249.089 pascals.
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 pascal?
The SI unit: one newton per square metre.
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 Pa in my head?
Plenty of people do this in their head: multiply by 250 instead of using the exact factor 249.0889. At 100 that shortcut gives 25,000 pascals, off by 91.11 pascals or about 0.37%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Inches Of Water to pascals reference tables
| Inches Of Water | Pascals |
|---|---|
| 0.5 inH₂O | 124.544 Pa |
| 1 inH₂O | 249.089 Pa |
| 2 inH₂O | 498.178 Pa |
| 3 inH₂O | 747.267 Pa |
| 5 inH₂O | 1245.44 Pa |
| 10 inH₂O | 2490.89 Pa |
| 20 inH₂O | 4981.78 Pa |
| 25 inH₂O | 6227.22 Pa |
| 50 inH₂O | 12,454.4 Pa |
| 75 inH₂O | 18,681.7 Pa |
| 100 inH₂O | 24,908.9 Pa |
| 250 inH₂O | 62,272.2 Pa |
| 500 inH₂O | 124,544 Pa |
| 1000 inH₂O | 249,089 Pa |
| 5000 inH₂O | 1.24544e+06 Pa |
Exact factor: 1 inch of water = 249.0889 pascals.
| Quantity | inH₂O | Pa |
|---|---|---|
| Sea-level air | 406.8 inH₂O | 1.013e+05 Pa |
| A car tyre | 885.8 inH₂O | 2.206e+05 Pa |
| Blood pressure, systolic | 64.23 inH₂O | 1.6e+04 Pa |
| A bicycle tyre | 2491 inH₂O | 6.205e+05 Pa |
| A domestic water main | 1606 inH₂O | 4e+05 Pa |
| A steam boiler | 4015 inH₂O | 1e+06 Pa |
Published reference values, converted with the same factor this page uses.