The calculated distance (air line) between Saint-Valery-en-Caux and Rennes is approximately 163 miles respectively 263 kilometers.
By car or train, the actual journey to Rennes is certainly longer, as only the direct route (as the crow flies) between Saint-Valery-en-Caux and Rennes has been calculated here.
Air line (approximately)
263 kilometers
142 nautical miles