The calculated distance (air line) between Sơn Tây and Dien Bien Phu is approximately 161 miles respectively 259 kilometers.
By car or train, the actual journey to Dien Bien Phu is certainly longer, as only the direct route (as the crow flies) between Sơn Tây and Dien Bien Phu has been calculated here.
Air line (approximately)
259 kilometers
140 nautical miles