Nautical miles per day to miles per hour conversion calculator shown above calculates how many miles per hour are in 'X' nautical miles per day (where 'X' is the number of nautical miles per day to convert to miles per hour). In order to convert a value from nautical miles per day to miles per hour (from nmi/d to mph) simply type the number of nmi/d to be converted to mph and then click on the 'convert' button.