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