This page converts inches of water into inches of mercury using the factor 0.07355590276, 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. 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. 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 mercury so the number you get has something to be compared against.
The formula
inches of water- The amount you are converting, in inches of water
0.0735559027625- The exact number of inches of mercury in one inch of water
inches of mercury- The converted result
How it works, step by step
- Enter the value in inches of water.
- It is multiplied by 0.0735559027625, 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 domestic water main: 1610 inH₂O in inches of mercury
Take a domestic water main, roughly 1610 inH₂O. The conversion is a single multiplication — 1610 × 0.0735559 — giving 118.425 inHg. Because the relationship is proportional, doubling the input doubles the answer to 236.85 inHg.
Sea-level air: 407 inH₂O in inches of mercury
Take sea-level air, roughly 407 inH₂O. The conversion is a single multiplication — 407 × 0.0735559 — giving 29.9373 inHg. Because the relationship is proportional, doubling the input doubles the answer to 59.8745 inHg.
How to read your score
Frequently asked questions
How many inches of mercury are in one inch of water?
Exactly 0.0735559027625. 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 inches of mercury?
inches of mercury = inches of water × 0.0735559027625. Reversed, inches of water = inches of mercury ÷ 0.0735559027625, which is the same as multiplying by 13.5951019897.
Which is the bigger unit, the inch of water or the inch of mercury?
The inch of mercury. One inch of water is only 0.0735559 of a inch of mercury, so it takes 13.5951 inches 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 inch of water?
The low-pressure unit for duct static pressure and gas appliances in the US.
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 inH₂O to inHg in my head?
Plenty of people do this in their head: divide by 14 instead of using the exact factor 0.07355590276. At 100 that shortcut gives 7.1428571 inches of mercury, off by 0.2127 inches of mercury or about 2.89%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Inches Of Water to inches of mercury reference tables
| Inches Of Water | Inches Of Mercury |
|---|---|
| 0.5 inH₂O | 0.036778 inHg |
| 1 inH₂O | 0.0735559 inHg |
| 2 inH₂O | 0.147112 inHg |
| 3 inH₂O | 0.220668 inHg |
| 5 inH₂O | 0.36778 inHg |
| 10 inH₂O | 0.735559 inHg |
| 20 inH₂O | 1.47112 inHg |
| 25 inH₂O | 1.8389 inHg |
| 50 inH₂O | 3.6778 inHg |
| 75 inH₂O | 5.51669 inHg |
| 100 inH₂O | 7.35559 inHg |
| 250 inH₂O | 18.389 inHg |
| 500 inH₂O | 36.778 inHg |
| 1000 inH₂O | 73.5559 inHg |
| 5000 inH₂O | 367.78 inHg |
Exact factor: 1 inch of water = 0.0735559027625 inches of mercury.
| Quantity | inH₂O | inHg |
|---|---|---|
| Sea-level air | 406.8 inH₂O | 29.92 inHg |
| A car tyre | 885.8 inH₂O | 65.15 inHg |
| Blood pressure, systolic | 64.23 inH₂O | 4.724 inHg |
| A bicycle tyre | 2491 inH₂O | 183.2 inHg |
| A domestic water main | 1606 inH₂O | 118.1 inHg |
| A steam boiler | 4015 inH₂O | 295.3 inHg |
Published reference values, converted with the same factor this page uses.