Centimeters of water to millimeters of water converter above calculates how many millimeters of water are in 'X' centimeters of water (where 'X' is the number of centimeters of water to convert to millimeters of water). In order to convert a value from centimeters of water to millimeters of water (from cmH2O to mmH2O) simply type the number of cmH2O to be converted to mmH2O and then click on the 'convert' button.