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