The calculated distance (air line) between Soisy-sous-Montmorency and Écouen is approximately 4 miles respectively 7 kilometers.
By car or train, the actual journey to Écouen is certainly longer, as only the direct route (as the crow flies) between Soisy-sous-Montmorency and Écouen has been calculated here.
Air line (approximately)
7 kilometers
4 nautical miles