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