The calculated distance (air line) between Dortmund and Marburg an der Lahn is approximately 75 miles respectively 120 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 Dortmund and Marburg an der Lahn has been calculated here.
Air line (approximately)
120 kilometers
65 nautical miles