The calculated distance (air line) between Castelnovo di Sotto and San Martino in Rio is approximately 12 miles respectively 19 kilometers.
By car or train, the actual journey to San Martino in Rio is certainly longer, as only the direct route (as the crow flies) between Castelnovo di Sotto and San Martino in Rio has been calculated here.
Air line (approximately)
19 kilometers
10 nautical miles