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