The calculated distance (air line) between Frankfurt am Main and Ludwigshafen am Rhein is approximately 45 miles respectively 73 kilometers.
By car or train, the actual journey to Ludwigshafen am Rhein is certainly longer, as only the direct route (as the crow flies) between Frankfurt am Main and Ludwigshafen am Rhein has been calculated here.
Air line (approximately)
73 kilometers
39 nautical miles