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