The calculated distance (air line) between Niigata and Ryōtsu-minato is approximately 34 miles respectively 54 kilometers.
By car or train, the actual journey to Ryōtsu-minato is certainly longer, as only the direct route (as the crow flies) between Niigata and Ryōtsu-minato has been calculated here.
Air line (approximately)
54 kilometers
29 nautical miles