To convert inches of mercury to feet of water, multiply by 1.132925128. That factor is the whole relationship: both units measure pressure, so the conversion is a proportion with no offset and no substance-specific constant.
US aviation and weather altimeter setting unit. 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. Below the calculator there is a step table for the values people look up most, and a second table putting real pressure figures into feet of water so the number you get has something to be compared against.
The formula
inches of mercury- The amount you are converting, in inches of mercury
1.13292512791- The exact number of feet of water in one inch of mercury
feet of water- The converted result
How it works, step by step
- Enter the value in inches of mercury.
- It is multiplied by 1.13292512791, the exact factor between the two units.
- The answer is shown in feet of water, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
A domestic water main: 118 inHg in feet of water
A domestic water main comes to about 118 inHg. Multiplying by the factor: 118 × 1.13293 = 133.685 ftH₂O. Dividing the answer back by 1.13293 returns the figure you started with, which is the quickest way to check you have the factor the right way up.
Sea-level air: 29.9 inHg in feet of water
Sea-level air comes to about 29.9 inHg. Multiplying by the factor: 29.9 × 1.13293 = 33.8745 ftH₂O. Dividing the answer back by 1.13293 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 feet of water are in one inch of mercury?
Exactly 1.13292512791. 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 mercury to feet of water?
feet of water = inches of mercury × 1.13292512791. Reversed, inches of mercury = feet of water ÷ 1.13292512791, which is the same as multiplying by 0.88267086268.
Which is the bigger unit, the inch of mercury or the foot of water?
The inch of mercury. One inch of mercury equals 1.13293 feet 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 inch of mercury?
US aviation and weather altimeter setting unit.
What is a foot of water?
Pump head expressed as a column of water — the way pump curves are drawn.
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 inHg to ftH₂O in my head?
Plenty of people do this in their head: multiply by 1.1 instead of using the exact factor 1.132925128. At 100 that shortcut gives 110 feet of water, off by 3.293 feet of water or about 2.91%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Inches Of Mercury to feet of water reference tables
| Inches Of Mercury | Feet Of Water |
|---|---|
| 0.5 inHg | 0.566463 ftH₂O |
| 1 inHg | 1.13293 ftH₂O |
| 2 inHg | 2.26585 ftH₂O |
| 3 inHg | 3.39878 ftH₂O |
| 5 inHg | 5.66463 ftH₂O |
| 10 inHg | 11.3293 ftH₂O |
| 20 inHg | 22.6585 ftH₂O |
| 25 inHg | 28.3231 ftH₂O |
| 50 inHg | 56.6463 ftH₂O |
| 75 inHg | 84.9694 ftH₂O |
| 100 inHg | 113.293 ftH₂O |
| 250 inHg | 283.231 ftH₂O |
| 500 inHg | 566.463 ftH₂O |
| 1000 inHg | 1132.93 ftH₂O |
| 5000 inHg | 5664.63 ftH₂O |
Exact factor: 1 inch of mercury = 1.13292512791 feet of water.
| Quantity | inHg | ftH₂O |
|---|---|---|
| Sea-level air | 29.92 inHg | 33.9 ftH₂O |
| A car tyre | 65.15 inHg | 73.81 ftH₂O |
| Blood pressure, systolic | 4.724 inHg | 5.352 ftH₂O |
| A bicycle tyre | 183.2 inHg | 207.6 ftH₂O |
| A domestic water main | 118.1 inHg | 133.8 ftH₂O |
| A steam boiler | 295.3 inHg | 334.6 ftH₂O |
Published reference values, converted with the same factor this page uses.