The calculated distance (air line) between Mitsukaidō and Ryūgasaki is approximately 14 miles respectively 22 kilometers.
By car or train, the actual journey to Ryūgasaki is certainly longer, as only the direct route (as the crow flies) between Mitsukaidō and Ryūgasaki has been calculated here.
Air line (approximately)
22 kilometers
12 nautical miles