The calculated distance (air line) between Saint-Quentin-en-Yvelines and Croissy-sur-Seine is approximately 9 miles respectively 15 kilometers.
By car or train, the actual journey to Croissy-sur-Seine is certainly longer, as only the direct route (as the crow flies) between Saint-Quentin-en-Yvelines and Croissy-sur-Seine has been calculated here.
Air line (approximately)
15 kilometers
8 nautical miles