Bundesautobahn 643 (translates from German as Federal Motorway 643, short form Autobahn 643, abbreviated as BAB 643 or A 643) is a 8.4-kilometer (5.2 mi) short autobahn in Germany.

It is one of two autobahns in Germany that connect two neighboring state capitals in only one exit.

It is an important connection between Autobahn 66 on the north bank of the Rhine and A 60 south of Mainz.

This interchange also includes an exit ramp to Erich-Ollenhauser Straße (K 655), which leads northwest to Wiesbaden-Dotzheim and southeast to Biebrich.

It crosses the border with Rhineland-Palatinate on the Rhine with the Schierstein Bridge.