The calculated distance (air line) between Saint-Quentin-en-Yvelines and Aulnay-sous-Bois is approximately 24 miles respectively 39 kilometers.
By car or train, the actual journey to Aulnay-sous-Bois is certainly longer, as only the direct route (as the crow flies) between Saint-Quentin-en-Yvelines and Aulnay-sous-Bois has been calculated here.
Air line (approximately)
39 kilometers
21 nautical miles