Decibars to millimeters of mercury conversion calculator shown above calculates how many millimeters of mercury are in 'X' decibars (where 'X' is the number of decibars to convert to millimeters of mercury). In order to convert a value from decibars to millimeters of mercury (from dbar to mmHg) type the number of dbar to be converted to mmHg and then click on the 'convert' button.