The calculated distance (air line) between Saint-Ouen-l'Aumône and Rennes is approximately 185 miles respectively 298 kilometers.
By car or train, the actual journey to Rennes is certainly longer, as only the direct route (as the crow flies) between Saint-Ouen-l'Aumône and Rennes has been calculated here.
Air line (approximately)
298 kilometers
161 nautical miles