The calculated distance (air line) between Saint-Sébastien-sur-Loire and Le Havre is approximately 174 miles respectively 281 kilometers.
By car or train, the actual journey to Le Havre is certainly longer, as only the direct route (as the crow flies) between Saint-Sébastien-sur-Loire and Le Havre has been calculated here.
Air line (approximately)
281 kilometers
151 nautical miles