The calculated distance (air line) between Rennes and Boulogne-Billancourt is approximately 186 miles respectively 300 kilometers.
By car or train, the actual journey to Boulogne-Billancourt is certainly longer, as only the direct route (as the crow flies) between Rennes and Boulogne-Billancourt has been calculated here.
Air line (approximately)
300 kilometers
162 nautical miles