This page converts inches of water into millimeters of mercury using the factor 1.868320129, 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. The clinical unit for blood pressure worldwide.
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 millimeters 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
1.8683201286- The exact number of millimeters of mercury in one inch of water
millimeters of mercury- The converted result
How it works, step by step
- Enter the value in inches of water.
- It is multiplied by 1.8683201286, the exact factor between the two units.
- The answer is shown in millimeters of mercury, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
A bicycle tyre: 2490 inH₂O in millimeters of mercury
A bicycle tyre comes to about 2490 inH₂O. Multiplying by the factor: 2490 × 1.86832 = 4652.12 mmHg. Dividing the answer back by 1.86832 returns the figure you started with, which is the quickest way to check you have the factor the right way up.
A car tyre: 886 inH₂O in millimeters of mercury
Take a car tyre, roughly 886 inH₂O. The conversion is a single multiplication — 886 × 1.86832 — giving 1655.33 mmHg. Because the relationship is proportional, doubling the input doubles the answer to 3310.66 mmHg.
How to read your score
Frequently asked questions
How many millimeters of mercury are in one inch of water?
Exactly 1.8683201286. 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 millimeters of mercury?
millimeters of mercury = inches of water × 1.8683201286. Reversed, inches of water = millimeters of mercury ÷ 1.8683201286, which is the same as multiplying by 0.535240178968.
Which is the bigger unit, the inch of water or the millimeter of mercury?
The inch of water. One inch of water equals 1.86832 millimeters 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 millimeter of mercury?
The clinical unit for blood pressure worldwide.
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 mmHg in my head?
Plenty of people do this in their head: multiply by 1.9 instead of using the exact factor 1.868320129. At 100 that shortcut gives 190 millimeters of mercury, off by 3.168 millimeters of mercury or about 1.70%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Inches Of Water to millimeters of mercury reference tables
| Inches Of Water | Millimeters Of Mercury |
|---|---|
| 0.5 inH₂O | 0.93416 mmHg |
| 1 inH₂O | 1.86832 mmHg |
| 2 inH₂O | 3.73664 mmHg |
| 3 inH₂O | 5.60496 mmHg |
| 5 inH₂O | 9.3416 mmHg |
| 10 inH₂O | 18.6832 mmHg |
| 20 inH₂O | 37.3664 mmHg |
| 25 inH₂O | 46.708 mmHg |
| 50 inH₂O | 93.416 mmHg |
| 75 inH₂O | 140.124 mmHg |
| 100 inH₂O | 186.832 mmHg |
| 250 inH₂O | 467.08 mmHg |
| 500 inH₂O | 934.16 mmHg |
| 1000 inH₂O | 1868.32 mmHg |
| 5000 inH₂O | 9341.6 mmHg |
Exact factor: 1 inch of water = 1.8683201286 millimeters of mercury.
| Quantity | inH₂O | mmHg |
|---|---|---|
| Sea-level air | 406.8 inH₂O | 760 mmHg |
| A car tyre | 885.8 inH₂O | 1655 mmHg |
| Blood pressure, systolic | 64.23 inH₂O | 120 mmHg |
| A bicycle tyre | 2491 inH₂O | 4654 mmHg |
| A domestic water main | 1606 inH₂O | 3000 mmHg |
| A steam boiler | 4015 inH₂O | 7501 mmHg |
Published reference values, converted with the same factor this page uses.