A centimetre of water (US spelling centimeter of water, abbreviated cmH2O or cm H2O) is a less commonly used unit of pressure derived from pressure head calculations using metrology. It is frequently used to measure the central venous pressure, the intracranial pressure while sampling cerebrospinal fluid, as well as determining pressures during mechanical ventilation or in water supply networks (then usually in metres water column). It is also a common unit of pressure in the speech sciences.
It is defined as the pressure exerted by a column of water of 1 cm in height at 4 °C (temperature of maximum density) at the standard acceleration of gravity.
This unit is commonly used to specify the pressure to which a CPAP machine is set after a polysomnogram.
| 1 cmH2O | = 98.0638 pascals |
| = 0.01 metres water column or meters, water gauge (m.Wg) | |
| = 10 mm.Wg | |
| ≈ 0.98064 mbar or hectopascals | |
| ≈ 0.39370 inH2O | |
| ≈ 0.00096781 atm | |
| ≈ 0.73554 torr | |
| ≈ 0.73554 mmHg | |
| ≈ 0.028958 inHg | |
| ≈ 0.014223 psi |