This page converts feet of water into inches of mercury using the factor 0.8826708627, and shows the reverse figure alongside it. Both units measure pressure, which is why one number does the whole job.
Pump head expressed as a column of water — the way pump curves are drawn. US aviation and weather altimeter setting unit.
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 inches of mercury, so you can sanity-check whether your answer is a plausible size.
The formula
feet of water- The amount you are converting, in feet of water
0.88267086268- The exact number of inches of mercury in one foot of water
inches of mercury- The converted result
How it works, step by step
- Enter the value in feet of water.
- It is multiplied by 0.88267086268, the exact factor between the two units.
- The answer is shown in inches of mercury, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
A car tyre: 73.8 ftH₂O in inches of mercury
Take a car tyre, roughly 73.8 ftH₂O. The conversion is a single multiplication — 73.8 × 0.882671 — giving 65.1411 inHg. Because the relationship is proportional, doubling the input doubles the answer to 130.282 inHg.
Sea-level air: 33.9 ftH₂O in inches of mercury
At 33.9 ftH₂O (sea-level air), the same quantity in inches of mercury is 33.9 × 0.882671 = 29.9225 inHg. One foot of water is 0.882671 inches of mercury, so the numbers shrink as expected.
How to read your score
Frequently asked questions
How many inches of mercury are in one foot of water?
Exactly 0.88267086268. 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 inches of mercury?
inches of mercury = feet of water × 0.88267086268. Reversed, feet of water = inches of mercury ÷ 0.88267086268, which is the same as multiplying by 1.13292512791.
Which is the bigger unit, the foot of water or the inch of mercury?
The inch of mercury. One foot of water is only 0.882671 of a inch of mercury, so it takes 1.13293 feet of water to make one inch of mercury.
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 inch of mercury?
US aviation and weather altimeter setting unit.
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 inHg in my head?
Plenty of people do this in their head: divide by 1.1 instead of using the exact factor 0.8826708627. At 100 that shortcut gives 90.909091 inches of mercury, off by 2.642 inches of mercury or about 2.99%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Feet Of Water to inches of mercury reference tables
| Feet Of Water | Inches Of Mercury |
|---|---|
| 0.5 ftH₂O | 0.441335 inHg |
| 1 ftH₂O | 0.882671 inHg |
| 2 ftH₂O | 1.76534 inHg |
| 3 ftH₂O | 2.64801 inHg |
| 5 ftH₂O | 4.41335 inHg |
| 10 ftH₂O | 8.82671 inHg |
| 20 ftH₂O | 17.6534 inHg |
| 25 ftH₂O | 22.0668 inHg |
| 50 ftH₂O | 44.1335 inHg |
| 75 ftH₂O | 66.2003 inHg |
| 100 ftH₂O | 88.2671 inHg |
| 250 ftH₂O | 220.668 inHg |
| 500 ftH₂O | 441.335 inHg |
| 1000 ftH₂O | 882.671 inHg |
| 5000 ftH₂O | 4413.35 inHg |
Exact factor: 1 foot of water = 0.88267086268 inches of mercury.
| Quantity | ftH₂O | inHg |
|---|---|---|
| Sea-level air | 33.9 ftH₂O | 29.92 inHg |
| A car tyre | 73.81 ftH₂O | 65.15 inHg |
| Blood pressure, systolic | 5.352 ftH₂O | 4.724 inHg |
| A bicycle tyre | 207.6 ftH₂O | 183.2 inHg |
| A domestic water main | 133.8 ftH₂O | 118.1 inHg |
| A steam boiler | 334.6 ftH₂O | 295.3 inHg |
Published reference values, converted with the same factor this page uses.