The calculated distance (air line) between Saint-Ouen-l'Aumône and Rouen is approximately 54 miles respectively 86 kilometers.
By car or train, the actual journey to Rouen is certainly longer, as only the direct route (as the crow flies) between Saint-Ouen-l'Aumône and Rouen has been calculated here.
Air line (approximately)
86 kilometers
47 nautical miles