The calculated distance (air line) between Hainburg an der Donau and Donaustadt is approximately 23 miles respectively 37 kilometers.
By car or train, the actual journey to Donaustadt is certainly longer, as only the direct route (as the crow flies) between Hainburg an der Donau and Donaustadt has been calculated here.
Air line (approximately)
37 kilometers
20 nautical miles