This page converts inches of water into bar using the factor 0.002490889, and shows the reverse figure alongside it. Both units measure pressure, which is why one number does the whole job.
The low-pressure unit for duct static pressure and gas appliances in the US. Almost exactly atmospheric pressure; standard in European industry and diving.
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 bar, 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
0.002490889- The exact number of bar in one inch of water
bar- The converted result
How it works, step by step
- Enter the value in inches of water.
- It is multiplied by 0.002490889, the exact factor between the two units.
- The answer is shown in bar, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
Blood pressure, systolic: 64.2 inH₂O in bar
Blood pressure, systolic comes to about 64.2 inH₂O. Multiplying by the factor: 64.2 × 0.00249089 = 0.159915 bar. Dividing the answer back by 0.00249089 returns the figure you started with, which is the quickest way to check you have the factor the right way up.
A bicycle tyre: 2490 inH₂O in bar
At 2490 inH₂O (a bicycle tyre), the same quantity in bar is 2490 × 0.00249089 = 6.20231 bar. One inch of water is 0.00249089 bar, so the numbers shrink as expected.
How to read your score
Frequently asked questions
How many bar are in one inch of water?
Exactly 0.002490889. 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 bar?
bar = inches of water × 0.002490889. Reversed, inches of water = bar ÷ 0.002490889, which is the same as multiplying by 401.463092093.
Which is the bigger unit, the inch of water or the bar?
The bar. One inch of water is only 0.00249089 of a bar, so it takes 401.463 inches of water to make one bar.
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 bar?
Almost exactly atmospheric pressure; standard in European industry and diving.
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 bar in my head?
Plenty of people do this in their head: divide by 400 instead of using the exact factor 0.002490889. At 100 that shortcut gives 0.25 bar, off by 0.0009111 bar or about 0.37%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Inches Of Water to bar reference tables
| Inches Of Water | Bar |
|---|---|
| 0.5 inH₂O | 0.00124544 bar |
| 1 inH₂O | 0.00249089 bar |
| 2 inH₂O | 0.00498178 bar |
| 3 inH₂O | 0.00747267 bar |
| 5 inH₂O | 0.0124544 bar |
| 10 inH₂O | 0.0249089 bar |
| 20 inH₂O | 0.0498178 bar |
| 25 inH₂O | 0.0622722 bar |
| 50 inH₂O | 0.124544 bar |
| 75 inH₂O | 0.186817 bar |
| 100 inH₂O | 0.249089 bar |
| 250 inH₂O | 0.622722 bar |
| 500 inH₂O | 1.24544 bar |
| 1000 inH₂O | 2.49089 bar |
| 5000 inH₂O | 12.4544 bar |
Exact factor: 1 inch of water = 0.002490889 bar.
| Quantity | inH₂O | bar |
|---|---|---|
| Sea-level air | 406.8 inH₂O | 1.013 bar |
| A car tyre | 885.8 inH₂O | 2.206 bar |
| Blood pressure, systolic | 64.23 inH₂O | 0.16 bar |
| A bicycle tyre | 2491 inH₂O | 6.205 bar |
| A domestic water main | 1606 inH₂O | 4 bar |
| A steam boiler | 4015 inH₂O | 10 bar |
Published reference values, converted with the same factor this page uses.