The calculated distance (air line) between Neustadt an der Donau and Karlsruhe is approximately 153 miles respectively 247 kilometers.
By car or train, the actual journey to Karlsruhe is certainly longer, as only the direct route (as the crow flies) between Neustadt an der Donau and Karlsruhe has been calculated here.
Air line (approximately)
247 kilometers
133 nautical miles