Millibars to centimeters of water conversion calculator shown above calculates how many centimeters of water are in 'X' millibars (where 'X' is the number of millibars to convert to centimeters of water). In order to convert a value from millibars to centimeters of water (from mbar to cmH2O) simply type the number of mbar to be converted to cmH2O and then click on the 'convert' button.