This page converts millimeters of mercury into inches of water using the factor 0.535240179, and shows the reverse figure alongside it. Both units measure pressure, which is why one number does the whole job.
The clinical unit for blood pressure worldwide. The low-pressure unit for duct static pressure and gas appliances in the US.
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 inches of water, which is usually more useful than the bare number.
The formula
millimeters of mercury- The amount you are converting, in millimeters of mercury
0.535240178968- The exact number of inches of water in one millimeter of mercury
inches of water- The converted result
How it works, step by step
- Enter the value in millimeters of mercury.
- It is multiplied by 0.535240178968, the exact factor between the two units.
- The answer is shown in inches of water, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
Blood pressure, systolic: 120 mmHg in inches of water
At 120 mmHg (blood pressure, systolic), the same quantity in inches of water is 120 × 0.53524 = 64.2288 inH₂O. One millimeter of mercury is 0.53524 inches of water, so the numbers shrink as expected.
A car tyre: 1650 mmHg in inches of water
A car tyre comes to about 1650 mmHg. Multiplying by the factor: 1650 × 0.53524 = 883.146 inH₂O. Dividing the answer back by 0.53524 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 inches of water are in one millimeter of mercury?
Exactly 0.535240178968. 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 millimeters of mercury to inches of water?
inches of water = millimeters of mercury × 0.535240178968. Reversed, millimeters of mercury = inches of water ÷ 0.535240178968, which is the same as multiplying by 1.8683201286.
Which is the bigger unit, the millimeter of mercury or the inch of water?
The inch of water. One millimeter of mercury is only 0.53524 of a inch of water, so it takes 1.86832 millimeters of mercury to make one inch 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 millimeter of mercury?
The clinical unit for blood pressure worldwide.
What is a inch of water?
The low-pressure unit for duct static pressure and gas appliances in the US.
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 mmHg to inH₂O in my head?
Plenty of people do this in their head: divide by 1.9 instead of using the exact factor 0.535240179. At 100 that shortcut gives 52.631579 inches of water, off by 0.8924 inches of water or about 1.67%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Millimeters Of Mercury to inches of water reference tables
| Millimeters Of Mercury | Inches Of Water |
|---|---|
| 0.5 mmHg | 0.26762 inH₂O |
| 1 mmHg | 0.53524 inH₂O |
| 2 mmHg | 1.07048 inH₂O |
| 3 mmHg | 1.60572 inH₂O |
| 5 mmHg | 2.6762 inH₂O |
| 10 mmHg | 5.3524 inH₂O |
| 20 mmHg | 10.7048 inH₂O |
| 25 mmHg | 13.381 inH₂O |
| 50 mmHg | 26.762 inH₂O |
| 75 mmHg | 40.143 inH₂O |
| 100 mmHg | 53.524 inH₂O |
| 250 mmHg | 133.81 inH₂O |
| 500 mmHg | 267.62 inH₂O |
| 1000 mmHg | 535.24 inH₂O |
| 5000 mmHg | 2676.2 inH₂O |
Exact factor: 1 millimeter of mercury = 0.535240178968 inches of water.
| Quantity | mmHg | inH₂O |
|---|---|---|
| Sea-level air | 760 mmHg | 406.8 inH₂O |
| A car tyre | 1655 mmHg | 885.8 inH₂O |
| Blood pressure, systolic | 120 mmHg | 64.23 inH₂O |
| A bicycle tyre | 4654 mmHg | 2491 inH₂O |
| A domestic water main | 3000 mmHg | 1606 inH₂O |
| A steam boiler | 7501 mmHg | 4015 inH₂O |
Published reference values, converted with the same factor this page uses.