The calculated distance (air line) between Saint-Germain-en-Laye and Rouen is approximately 59 miles respectively 94 kilometers.
By car or train, the actual journey to Rouen is certainly longer, as only the direct route (as the crow flies) between Saint-Germain-en-Laye and Rouen has been calculated here.
Air line (approximately)
94 kilometers
51 nautical miles