Travel by Car: The driving distance between Frankfurt am Main and Mostar following fastest route is 1.400 km, and estimated travel time is around 13 hours. Recommended route goes via highway trough Croatia, Slovenia, Austria and Germany.
Alternative ways of travelling from Frankfurt am Main to Mostar:
Travel by train: It is possible to travel by train from Frankfurt am Main to Mostar but in total travelling time will be much longer compared to travel by car or bus. More information for travelling by train in Bosnia and Herzegovina you can check here.
Travel by plane: There is no direct flight, but there is option to fly from Split.
Map with buses from Mostar: