Understanding centimeters of mercury to centimeters of water Conversion
A centimeter of mercury (cmHg) is the pressure from a 1 cm mercury column, about 1333.2 pascals. A centimeter of water (cmH2O) is the much smaller pressure from a 1 cm column of water, about 98.07 pascals, widely used in respiratory medicine, ventilator settings, and low-pressure fluid systems. Because mercury is roughly 13.6 times denser than water, cmHg readings translate to far larger cmH2O values, which matters in medical and hydraulic manometry.
Conversion Formula
To convert centimeters of mercury to centimeters of water, multiply by this factor:
Step-by-Step Example
Convert 25 centimeters of mercury to centimeters of water.
How to Convert centimeters of mercury to centimeters of water
Because mercury is far denser than water, cmHg values grow by about 13.6 times when expressed in cmH2O.
- Take the cmHg reading: For example, 25 cmHg.
- Multiply by the factor: Apply 13.5951 centimeters of water per centimeter of mercury.
- Compute: .
- State the result: 25 centimeters of mercury equals about 339.878 centimeters of water.
centimeters of mercury to centimeters of water conversion table
| centimeters of mercury (cmHg) | centimeters of water (cmH2O) |
|---|---|
| 0 | 0 |
| 1 | 13.5951 |
| 2 | 27.1902 |
| 3 | 40.7853 |
| 4 | 54.3804 |
| 5 | 67.9755 |
| 6 | 81.5706 |
| 7 | 95.1657 |
| 8 | 108.7608 |
| 9 | 122.3559 |
| 10 | 135.951 |
| 15 | 203.9265 |
| 20 | 271.902 |
| 25 | 339.8775 |
| 30 | 407.853 |
| 40 | 543.804 |
| 50 | 679.755 |
| 60 | 815.706 |
| 70 | 951.657 |
| 80 | 1087.608 |
| 90 | 1223.559 |
| 100 | 1359.51 |
| 150 | 2039.265 |
| 200 | 2719.02 |
| 250 | 3398.775 |
| 300 | 4078.53 |
| 400 | 5438.04 |
| 500 | 6797.55 |
| 600 | 8157.06 |
| 700 | 9516.57 |
| 800 | 10876.08 |
| 900 | 12235.59 |
| 1000 | 13595.1 |
| 2000 | 27190.2 |
| 3000 | 40785.3 |
| 4000 | 54380.4 |
| 5000 | 67975.5 |
| 10000 | 135951 |
| 25000 | 339877.5 |
| 50000 | 679755 |
| 100000 | 1359510 |
| 250000 | 3398775 |
| 500000 | 6797550 |
| 1000000 | 13595100 |
What is the centimeter of mercury?
The centimeter of mercury (cmHg) is a unit of pressure equal to the pressure exerted by a one-centimeter-high column of mercury under standard conditions. It is a scaled-up form of the millimeter of mercury (torr) used in some scientific and industrial settings.
Definition
The conventional centimeter of mercury is based on a 1 cm column of mercury with a density of 13,595.1 kg/m³ under standard gravity (9.80665 m/s²):
Exactly, 1 cmHg = 1333.22387415 Pa, which is ten times the millimeter of mercury (1 mmHg ≈ 133.322 Pa). This equals 10 torr under the conventional definition.
Origin and History
The unit descends directly from Torricelli's mercury barometer of 1643, where atmospheric pressure was read as the height of a mercury column. Mercury's high density makes the column compact and easy to read. The conventional value fixes mercury's density (its value at 0 °C) and standard gravity so the unit is independent of temperature and location.
Law and Notable Facts
The centimeter of mercury is not an SI unit; the SI unit of pressure is the pascal. It relates to the standard atmosphere as 1 atm = 76 cmHg exactly (by the historical 760 mmHg definition). The millimeter of mercury (mmHg), essentially identical to the torr, remains standard in medicine for blood pressure.
Real-World Examples and Conversions
- 1 cmHg = 10 mmHg (10 torr) ≈ 1.33322 kPa.
- One standard atmosphere equals exactly 76 cmHg.
- A blood pressure of 120/80 mmHg corresponds to 12/8 cmHg.
- A vacuum of 5 cmHg absolute is about 6.7 kPa, roughly 93% below atmospheric pressure.
What is the centimeter of water?
The centimeter of water (cmH2O) is a unit of pressure equal to the pressure exerted by a one-centimeter-high column of water under standard conditions. It is used heavily in medicine and respiratory therapy, where small pressures are common.
Definition
The conventional centimeter of water is defined as the pressure of a 1 cm column of water with a density of 1000 kg/m³ under standard gravity (9.80665 m/s²):
This is the conventional value. Because water density varies with temperature, more precise variants exist (for example, cmH2O at 4 °C uses water's maximum density of about 999.972 kg/m³, giving roughly 98.064 Pa).
Origin and History
The unit comes directly from the water manometer, an instrument in which pressure is read as the height difference of a water column. Water was chosen for low pressures because it produces a taller, more readable column than mercury (water is about 13.6 times less dense). The convention fixes water density and gravity so the unit has a single agreed value independent of local conditions.
Law and Notable Facts
The centimeter of water is not an SI unit but is permitted in medical contexts, where it remains standard for measuring airway, ventilator, and cerebrospinal-fluid pressures. Roughly 1 cmH2O equals 0.7356 mmHg, so about 1.36 cmH2O make up 1 mmHg.
Real-World Examples and Conversions
- Mechanical ventilators typically deliver positive end-expiratory pressure (PEEP) of 5 to 10 cmH2O.
- Normal cerebrospinal-fluid opening pressure in a lumbar puncture is roughly 10 to 18 cmH2O.
- 1 cmH2O ≈ 98.0665 Pa ≈ 0.098 kPa.
- A standard atmosphere equals about 1033.2 cmH2O.
Frequently Asked Questions
How many centimeters of water equal one centimeter of mercury?
One centimeter of mercury equals 13.5951 centimeters of water, reflecting mercury's density of about 13.6 times that of water.
How many centimeters of mercury make one centimeter of water?
There are about 0.07355591 centimeters of mercury in one centimeter of water, the reciprocal of this factor.
Why is the factor close to 13.6?
Mercury is roughly 13.6 times denser than water, so a mercury column produces about 13.6 times the pressure of an equal-height water column.
Where is centimeters of water used?
The cmH2O unit is standard in respiratory therapy and ventilation, where airway and lung pressures are measured in centimeters of water.
How do I convert back to centimeters of mercury?
Multiply the cmH2O value by 0.07355591, or divide by 13.5951, to get centimeters of mercury.
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Complete centimeters of mercury conversion table
| Unit | Result |
|---|---|
| pascals (Pa) | 1333.224 Pa |
| kilopascals (kPa) | 1.333224 kPa |
| megapascals (MPa) | 0.001333224 MPa |
| hectopascals (hPa) | 13.33224 hPa |
| millibar (mbar) | 13.33224 mbar |
| bar (bar) | 0.01333224 bar |
| torr (torr) | 10 torr |
| meters of water @ 4°C (mH2O) | 0.135951 mH2O |
| millimeters of mercury (mmHg) | 10 mmHg |
| standard atmospheres (atm) | 0.0131579 atm |
| centimeters of water (cmH2O) | 13.5951 cmH2O |
| technical atmospheres (at) | 0.0135951 at |
| pounds per square inch (psi) | 0.1933678 psi |
| kilopound per square inch (ksi) | 0.0001933678 ksi |
| Inches of mercury (inHg) | 0.3937008 inHg |