Centimetre of water

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A centimeter (centimetre) of water or cm H₂O is a less commonly used unit of pressure. It is 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

To convert this measure to other units, the following conversion is used:

1 mmHg = 1.36 cmH₂O = 0.133 kPa = 0.0193 psi = 1.3332 mbar