The calculated distance (air line) between Caudebec-lès-Elbeuf and Rennes is approximately 147 miles respectively 237 kilometers.
By car or train, the actual journey to Rennes is certainly longer, as only the direct route (as the crow flies) between Caudebec-lès-Elbeuf and Rennes has been calculated here.
Air line (approximately)
237 kilometers
128 nautical miles