The calculated distance (air line) between Montreuil and Rosny-sous-Bois is approximately 3 miles respectively 4 kilometers.
By car or train, the actual journey to Rosny-sous-Bois is certainly longer, as only the direct route (as the crow flies) between Montreuil and Rosny-sous-Bois has been calculated here.
Air line (approximately)
4 kilometers
2 nautical miles