This page converts centimeters of water into inches of mercury using the factor 0.028959018, and shows the reverse figure alongside it. Both units measure pressure, which is why one number does the whole job.
US aviation and weather altimeter setting unit. The unit ventilator and CPAP pressures are set in.
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 mercury, which is usually more useful than the bare number.
The formula
centimeters of water- The amount you are converting, in centimeters of water
0.0289590179982- The exact number of inches of mercury in one centimeter of water
inches of mercury- The converted result
How it works, step by step
- Enter the value in centimeters of water.
- It is multiplied by 0.0289590179982, 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
Blood pressure, systolic: 163 cmH₂O in inches of mercury
Take blood pressure, systolic, roughly 163 cmH₂O. The conversion is a single multiplication — 163 × 0.028959 — giving 4.72032 inHg. Because the relationship is proportional, doubling the input doubles the answer to 9.44064 inHg.
A bicycle tyre: 6330 cmH₂O in inches of mercury
Take a bicycle tyre, roughly 6330 cmH₂O. The conversion is a single multiplication — 6330 × 0.028959 — giving 183.311 inHg. Because the relationship is proportional, doubling the input doubles the answer to 366.621 inHg.
How to read your score
Frequently asked questions
How many inches of mercury are in one centimeter of water?
Exactly 0.0289590179982. 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 centimeters of water to inches of mercury?
inches of mercury = centimeters of water × 0.0289590179982. Reversed, centimeters of water = inches of mercury ÷ 0.0289590179982, which is the same as multiplying by 34.5315576675.
Which is the bigger unit, the centimeter of water or the inch of mercury?
The inch of mercury. One centimeter of water is only 0.028959 of a inch of mercury, so it takes 34.5316 centimeters 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 centimeter of water?
The unit ventilator and CPAP pressures are set in.
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 cmH₂O to inHg in my head?
Plenty of people do this in their head: divide by 35 instead of using the exact factor 0.028959018. At 100 that shortcut gives 2.8571429 inches of mercury, off by 0.03876 inches of mercury or about 1.34%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Centimeters Of Water to inches of mercury reference tables
| Centimeters Of Water | Inches Of Mercury |
|---|---|
| 0.5 cmH₂O | 0.0144795 inHg |
| 1 cmH₂O | 0.028959 inHg |
| 2 cmH₂O | 0.057918 inHg |
| 3 cmH₂O | 0.0868771 inHg |
| 5 cmH₂O | 0.144795 inHg |
| 10 cmH₂O | 0.28959 inHg |
| 20 cmH₂O | 0.57918 inHg |
| 25 cmH₂O | 0.723975 inHg |
| 50 cmH₂O | 1.44795 inHg |
| 75 cmH₂O | 2.17193 inHg |
| 100 cmH₂O | 2.8959 inHg |
| 250 cmH₂O | 7.23975 inHg |
| 500 cmH₂O | 14.4795 inHg |
| 1000 cmH₂O | 28.959 inHg |
| 5000 cmH₂O | 144.795 inHg |
Exact factor: 1 centimeter of water = 0.0289590179982 inches of mercury.
| Quantity | cmH₂O | inHg |
|---|---|---|
| Sea-level air | 1033 cmH₂O | 29.92 inHg |
| A car tyre | 2250 cmH₂O | 65.15 inHg |
| Blood pressure, systolic | 163.1 cmH₂O | 4.724 inHg |
| A bicycle tyre | 6328 cmH₂O | 183.2 inHg |
| A domestic water main | 4079 cmH₂O | 118.1 inHg |
| A steam boiler | 1.02e+04 cmH₂O | 295.3 inHg |
Published reference values, converted with the same factor this page uses.