To convert millimeters of mercury to centimeters of water, multiply by 1.35951. That factor is the whole relationship: both units measure pressure, so the conversion is a proportion with no offset and no substance-specific constant.
The unit ventilator and CPAP pressures are set in. 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 centimeters of water so the number you get has something to be compared against.
The formula
millimeters of mercury- The amount you are converting, in millimeters of mercury
1.35951- The exact number of centimeters of water in one millimeter of mercury
centimeters of water- The converted result
How it works, step by step
- Enter the value in millimeters of mercury.
- It is multiplied by 1.35951, the exact factor between the two units.
- The answer is shown in centimeters of water, with the reverse conversion beneath it.
- Check the reference table if you want a figure of comparable size.
Worked examples
A car tyre: 1650 mmHg in centimeters of water
Take a car tyre, roughly 1650 mmHg. The conversion is a single multiplication — 1650 × 1.35951 — giving 2243.19 cmH₂O. Because the relationship is proportional, doubling the input doubles the answer to 4486.38 cmH₂O.
A bicycle tyre: 4650 mmHg in centimeters of water
Take a bicycle tyre, roughly 4650 mmHg. The conversion is a single multiplication — 4650 × 1.35951 — giving 6321.72 cmH₂O. Because the relationship is proportional, doubling the input doubles the answer to 12,643.4 cmH₂O.
How to read your score
Frequently asked questions
How many centimeters of water are in one millimeter of mercury?
Exactly 1.35951. 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 centimeters of water?
centimeters of water = millimeters of mercury × 1.35951. Reversed, millimeters of mercury = centimeters of water ÷ 1.35951, which is the same as multiplying by 0.735559135277.
Which is the bigger unit, the millimeter of mercury or the centimeter of water?
The millimeter of mercury. One millimeter of mercury equals 1.35951 centimeters 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 centimeter of water?
The unit ventilator and CPAP pressures are set in.
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 cmH₂O in my head?
Plenty of people do this in their head: multiply by 1.4 instead of using the exact factor 1.35951. At 100 that shortcut gives 140 centimeters of water, off by 4.049 centimeters of water or about 2.98%. Fine for a rough estimate, not fine for anything you are cutting to size or dosing.
Millimeters Of Mercury to centimeters of water reference tables
| Millimeters Of Mercury | Centimeters Of Water |
|---|---|
| 0.5 mmHg | 0.679755 cmH₂O |
| 1 mmHg | 1.35951 cmH₂O |
| 2 mmHg | 2.71902 cmH₂O |
| 3 mmHg | 4.07853 cmH₂O |
| 5 mmHg | 6.79755 cmH₂O |
| 10 mmHg | 13.5951 cmH₂O |
| 20 mmHg | 27.1902 cmH₂O |
| 25 mmHg | 33.9877 cmH₂O |
| 50 mmHg | 67.9755 cmH₂O |
| 75 mmHg | 101.963 cmH₂O |
| 100 mmHg | 135.951 cmH₂O |
| 250 mmHg | 339.877 cmH₂O |
| 500 mmHg | 679.755 cmH₂O |
| 1000 mmHg | 1359.51 cmH₂O |
| 5000 mmHg | 6797.55 cmH₂O |
Exact factor: 1 millimeter of mercury = 1.35951 centimeters of water.
| Quantity | mmHg | cmH₂O |
|---|---|---|
| Sea-level air | 760 mmHg | 1033 cmH₂O |
| A car tyre | 1655 mmHg | 2250 cmH₂O |
| Blood pressure, systolic | 120 mmHg | 163.1 cmH₂O |
| A bicycle tyre | 4654 mmHg | 6328 cmH₂O |
| A domestic water main | 3000 mmHg | 4079 cmH₂O |
| A steam boiler | 7501 mmHg | 1.02e+04 cmH₂O |
Published reference values, converted with the same factor this page uses.