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