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