The calculated distance (air line) between Dinard and Montfort-sur-Meu is approximately 35 miles respectively 56 kilometers.
By car or train, the actual journey to Montfort-sur-Meu is certainly longer, as only the direct route (as the crow flies) between Dinard and Montfort-sur-Meu has been calculated here.
Air line (approximately)
56 kilometers
30 nautical miles