The calculated distance (air line) between Bonn and Marburg an der Lahn is approximately 73 miles respectively 118 kilometers.
By car or train, the actual journey to Marburg an der Lahn is certainly longer, as only the direct route (as the crow flies) between Bonn and Marburg an der Lahn has been calculated here.
Air line (approximately)
118 kilometers
64 nautical miles