Centimetres of H2O

Centimeters of Water (cmH2O) Column is a manometric unit used to relate a pressure reading to the height of fresh water at a temperature of 4°C. 1 centimeter of water gauge equals 98.0665 pascals.

The cmH2O pressure unit is mostly used to measure breathing on respirators and ventilators which are used in medical and physiological applications such as controlling respiratory conditions or monitoring athletic performance.

There are many ways of writing centimeters of water, but the cause of most confusion are Water Column (WC) and Water Gauge (WG), which both mean exactly the same thing.

 The difference between cmH2O at 4°C and cmH2O at 20°C relates to the change in density of water between the two temperatures:

●       Density at 4°C = 1000 kg/m³

●       Density at 20°C = 998.2 kg/m³

Therefore a hydrostatic pressure of 1 cmH2O at 20°C is 998.20. So 1000 cmH2O at 4°C equals 0.9982 cmH2O at 20°C.