To convert inches of water to kilopascals, multiply by 0.2490889. 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 standard tyre-pressure unit in metric countries. 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. Two tables follow: rounded steps for quick lookup, and a set of real reference quantities converted into kilopascals, which is usually more useful than the bare number.
The formula
inches of water- The amount you are converting, in inches of water
0.2490889- The exact number of kilopascals in one inch of water
kilopascals- The converted result
How it works, step by step
- Enter the value in inches of water.
- It is multiplied by 0.2490889, the exact factor between the two units.
- The answer is shown in kilopascals, 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 kilopascals
Take a domestic water main, roughly 1610 inH₂O. The conversion is a single multiplication — 1610 × 0.249089 — giving 401.033 kPa. Because the relationship is proportional, doubling the input doubles the answer to 802.066 kPa.
A steam boiler: 4010 inH₂O in kilopascals
A steam boiler comes to about 4010 inH₂O. Multiplying by the factor: 4010 × 0.249089 = 998.846 kPa. Dividing the answer back by 0.249089 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 kilopascals are in one inch of water?
Exactly 0.2490889. 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 kilopascals?
kilopascals = inches of water × 0.2490889. Reversed, inches of water = kilopascals ÷ 0.2490889, which is the same as multiplying by 4.01463092093.
Which is the bigger unit, the inch of water or the kilopascal?
The kilopascal. One inch of water is only 0.249089 of a kilopascal, so it takes 4.01463 inches of water to make one kilopascal.
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 kilopascal?
The standard tyre-pressure unit in metric countries.
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 kPa in my head?
Plenty of people do this in their head: divide by 4 instead of using the exact factor 0.2490889. At 100 that shortcut gives 25 kilopascals, off by 0.09111 kilopascals or about 0.37%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Inches Of Water to kilopascals reference tables
| Inches Of Water | Kilopascals |
|---|---|
| 0.5 inH₂O | 0.124544 kPa |
| 1 inH₂O | 0.249089 kPa |
| 2 inH₂O | 0.498178 kPa |
| 3 inH₂O | 0.747267 kPa |
| 5 inH₂O | 1.24544 kPa |
| 10 inH₂O | 2.49089 kPa |
| 20 inH₂O | 4.98178 kPa |
| 25 inH₂O | 6.22722 kPa |
| 50 inH₂O | 12.4544 kPa |
| 75 inH₂O | 18.6817 kPa |
| 100 inH₂O | 24.9089 kPa |
| 250 inH₂O | 62.2722 kPa |
| 500 inH₂O | 124.544 kPa |
| 1000 inH₂O | 249.089 kPa |
| 5000 inH₂O | 1245.44 kPa |
Exact factor: 1 inch of water = 0.2490889 kilopascals.
| Quantity | inH₂O | kPa |
|---|---|---|
| Sea-level air | 406.8 inH₂O | 101.3 kPa |
| A car tyre | 885.8 inH₂O | 220.6 kPa |
| Blood pressure, systolic | 64.23 inH₂O | 16 kPa |
| A bicycle tyre | 2491 inH₂O | 620.5 kPa |
| A domestic water main | 1606 inH₂O | 400 kPa |
| A steam boiler | 4015 inH₂O | 1000 kPa |
Published reference values, converted with the same factor this page uses.