One millibar is exactly 0.4014630921 inches of water, so converting millibars to inches of water is a single multiplication. Enter any figure and the result appears as you type — the arithmetic runs in your browser, so nothing is sent anywhere.
The low-pressure unit for duct static pressure and gas appliances in the US. The meteorologist’s unit — sea-level pressure averages 1013.25 mbar.
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
millibars- The amount you are converting, in millibars
0.401463092093- The exact number of inches of water in one millibar
inches of water- The converted result
How it works, step by step
- Enter the value in millibars.
- It is multiplied by 0.401463092093, 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 steam boiler: 1e+04 mbar in inches of water
At 1e+04 mbar (a steam boiler), the same quantity in inches of water is 1e+04 × 0.401463 = 4014.63 inH₂O. One millibar is 0.401463 inches of water, so the numbers shrink as expected.
A bicycle tyre: 6210 mbar in inches of water
Take a bicycle tyre, roughly 6210 mbar. The conversion is a single multiplication — 6210 × 0.401463 — giving 2493.09 inH₂O. Because the relationship is proportional, doubling the input doubles the answer to 4986.17 inH₂O.
How to read your score
Frequently asked questions
How many inches of water are in one millibar?
Exactly 0.401463092093. 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 millibars to inches of water?
inches of water = millibars × 0.401463092093. Reversed, millibars = inches of water ÷ 0.401463092093, which is the same as multiplying by 2.490889.
Which is the bigger unit, the millibar or the inch of water?
The inch of water. One millibar is only 0.401463 of a inch of water, so it takes 2.49089 millibars to make one inch 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 millibar?
The meteorologist’s unit — sea-level pressure averages 1013.25 mbar.
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 mbar to inH₂O in my head?
Plenty of people do this in their head: divide by 2.5 instead of using the exact factor 0.4014630921. At 100 that shortcut gives 40 inches of water, off by 0.1463 inches of water or about 0.36%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Millibars to inches of water reference tables
| Millibars | Inches Of Water |
|---|---|
| 0.5 mbar | 0.200732 inH₂O |
| 1 mbar | 0.401463 inH₂O |
| 2 mbar | 0.802926 inH₂O |
| 3 mbar | 1.20439 inH₂O |
| 5 mbar | 2.00732 inH₂O |
| 10 mbar | 4.01463 inH₂O |
| 20 mbar | 8.02926 inH₂O |
| 25 mbar | 10.0366 inH₂O |
| 50 mbar | 20.0732 inH₂O |
| 75 mbar | 30.1097 inH₂O |
| 100 mbar | 40.1463 inH₂O |
| 250 mbar | 100.366 inH₂O |
| 500 mbar | 200.732 inH₂O |
| 1000 mbar | 401.463 inH₂O |
| 5000 mbar | 2007.32 inH₂O |
Exact factor: 1 millibar = 0.401463092093 inches of water.
| Quantity | mbar | inH₂O |
|---|---|---|
| Sea-level air | 1013 mbar | 406.8 inH₂O |
| A car tyre | 2206 mbar | 885.8 inH₂O |
| Blood pressure, systolic | 160 mbar | 64.23 inH₂O |
| A bicycle tyre | 6205 mbar | 2491 inH₂O |
| A domestic water main | 4000 mbar | 1606 inH₂O |
| A steam boiler | 1e+04 mbar | 4015 inH₂O |
Published reference values, converted with the same factor this page uses.