To convert inches of water to megapascals, multiply by 0.0002490889. That factor is the whole relationship: both units measure pressure, so the conversion is a proportion with no offset and no substance-specific constant.
Used for material strength and hydraulic systems. 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 megapascals, 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
0.0002490889- The exact number of megapascals in one inch of water
megapascals- The converted result
How it works, step by step
- Enter the value in inches of water.
- It is multiplied by 0.0002490889, the exact factor between the two units.
- The answer is shown in megapascals, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
A steam boiler: 4010 inH₂O in megapascals
A steam boiler comes to about 4010 inH₂O. Multiplying by the factor: 4010 × 0.000249089 = 0.998846 MPa. Dividing the answer back by 0.000249089 returns the figure you started with, which is the quickest way to check you have the factor the right way up.
A car tyre: 886 inH₂O in megapascals
At 886 inH₂O (a car tyre), the same quantity in megapascals is 886 × 0.000249089 = 0.220693 MPa. One inch of water is 0.000249089 megapascals, so the numbers shrink as expected.
How to read your score
Frequently asked questions
How many megapascals are in one inch of water?
Exactly 0.0002490889. 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 megapascals?
megapascals = inches of water × 0.0002490889. Reversed, inches of water = megapascals ÷ 0.0002490889, which is the same as multiplying by 4014.63092093.
Which is the bigger unit, the inch of water or the megapascal?
The megapascal. One inch of water is only 0.000249089 of a megapascal, so it takes 4014.63 inches of water to make one megapascal.
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 megapascal?
Used for material strength and hydraulic systems.
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 MPa in my head?
Plenty of people do this in their head: divide by 4000 instead of using the exact factor 0.0002490889. At 100 that shortcut gives 0.025 megapascals, off by 0.000091 megapascals or about 0.37%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Inches Of Water to megapascals reference tables
| Inches Of Water | Megapascals |
|---|---|
| 0.5 inH₂O | 0.000124544 MPa |
| 1 inH₂O | 0.000249089 MPa |
| 2 inH₂O | 0.000498178 MPa |
| 3 inH₂O | 0.000747267 MPa |
| 5 inH₂O | 0.00124544 MPa |
| 10 inH₂O | 0.00249089 MPa |
| 20 inH₂O | 0.00498178 MPa |
| 25 inH₂O | 0.00622722 MPa |
| 50 inH₂O | 0.0124544 MPa |
| 75 inH₂O | 0.0186817 MPa |
| 100 inH₂O | 0.0249089 MPa |
| 250 inH₂O | 0.0622722 MPa |
| 500 inH₂O | 0.124544 MPa |
| 1000 inH₂O | 0.249089 MPa |
| 5000 inH₂O | 1.24544 MPa |
Exact factor: 1 inch of water = 0.0002490889 megapascals.
| Quantity | inH₂O | MPa |
|---|---|---|
| Sea-level air | 406.8 inH₂O | 0.1013 MPa |
| A car tyre | 885.8 inH₂O | 0.2206 MPa |
| Blood pressure, systolic | 64.23 inH₂O | 0.016 MPa |
| A bicycle tyre | 2491 inH₂O | 0.6205 MPa |
| A domestic water main | 1606 inH₂O | 0.4 MPa |
| A steam boiler | 4015 inH₂O | 1 MPa |
Published reference values, converted with the same factor this page uses.