The calculated distance (air line) between Hérouville-Saint-Clair and Rennes is approximately 98 miles respectively 158 kilometers.
By car or train, the actual journey to Rennes is certainly longer, as only the direct route (as the crow flies) between Hérouville-Saint-Clair and Rennes has been calculated here.
Air line (approximately)
158 kilometers
85 nautical miles