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