The calculated distance (air line) between Sasso Marconi and Castel Maggiore is approximately 13 miles respectively 21 kilometers.
By car or train, the actual journey to Castel Maggiore is certainly longer, as only the direct route (as the crow flies) between Sasso Marconi and Castel Maggiore has been calculated here.
Air line (approximately)
21 kilometers
12 nautical miles