One foot of water is exactly 29.890669 millibars, so converting feet of water to millibars 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 meteorologist’s unit — sea-level pressure averages 1013.25 mbar. Pump head expressed as a column of water — the way pump curves are drawn.
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 millibars, which is usually more useful than the bare number.
The formula
feet of water- The amount you are converting, in feet of water
29.890669- The exact number of millibars in one foot of water
millibars- The converted result
How it works, step by step
- Enter the value in feet of water.
- It is multiplied by 29.890669, the exact factor between the two units.
- The answer is shown in millibars, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
A steam boiler: 335 ftH₂O in millibars
Take a steam boiler, roughly 335 ftH₂O. The conversion is a single multiplication — 335 × 29.8907 — giving 10,013.4 mbar. Because the relationship is proportional, doubling the input doubles the answer to 20,026.7 mbar.
Blood pressure, systolic: 5.35 ftH₂O in millibars
Take blood pressure, systolic, roughly 5.35 ftH₂O. The conversion is a single multiplication — 5.35 × 29.8907 — giving 159.915 mbar. Because the relationship is proportional, doubling the input doubles the answer to 319.83 mbar.
How to read your score
Frequently asked questions
How many millibars are in one foot of water?
Exactly 29.890669. 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 feet of water to millibars?
millibars = feet of water × 29.890669. Reversed, feet of water = millibars ÷ 29.890669, which is the same as multiplying by 0.0334552565551.
Which is the bigger unit, the foot of water or the millibar?
The foot of water. One foot of water equals 29.8907 millibars.
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 foot of water?
Pump head expressed as a column of water — the way pump curves are drawn.
What is a millibar?
The meteorologist’s unit — sea-level pressure averages 1013.25 mbar.
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 ftH₂O to mbar in my head?
Plenty of people do this in their head: multiply by 30 instead of using the exact factor 29.890669. At 100 that shortcut gives 3000 millibars, off by 10.93 millibars or about 0.37%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Feet Of Water to millibars reference tables
| Feet Of Water | Millibars |
|---|---|
| 0.5 ftH₂O | 14.9453 mbar |
| 1 ftH₂O | 29.8907 mbar |
| 2 ftH₂O | 59.7813 mbar |
| 3 ftH₂O | 89.672 mbar |
| 5 ftH₂O | 149.453 mbar |
| 10 ftH₂O | 298.907 mbar |
| 20 ftH₂O | 597.813 mbar |
| 25 ftH₂O | 747.267 mbar |
| 50 ftH₂O | 1494.53 mbar |
| 75 ftH₂O | 2241.8 mbar |
| 100 ftH₂O | 2989.07 mbar |
| 250 ftH₂O | 7472.67 mbar |
| 500 ftH₂O | 14,945.3 mbar |
| 1000 ftH₂O | 29,890.7 mbar |
| 5000 ftH₂O | 149,453 mbar |
Exact factor: 1 foot of water = 29.890669 millibars.
| Quantity | ftH₂O | mbar |
|---|---|---|
| Sea-level air | 33.9 ftH₂O | 1013 mbar |
| A car tyre | 73.81 ftH₂O | 2206 mbar |
| Blood pressure, systolic | 5.352 ftH₂O | 160 mbar |
| A bicycle tyre | 207.6 ftH₂O | 6205 mbar |
| A domestic water main | 133.8 ftH₂O | 4000 mbar |
| A steam boiler | 334.6 ftH₂O | 1e+04 mbar |
Published reference values, converted with the same factor this page uses.