The calculated distance (air line) between Dourdan and Saint-Quentin-en-Yvelines is approximately 17 miles respectively 27 kilometers.
By car or train, the actual journey to Saint-Quentin-en-Yvelines is certainly longer, as only the direct route (as the crow flies) between Dourdan and Saint-Quentin-en-Yvelines has been calculated here.
Air line (approximately)
27 kilometers
15 nautical miles