The calculated distance (air line) between Hà Đông and Dien Bien Phu is approximately 180 miles respectively 289 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 Hà Đông and Dien Bien Phu has been calculated here.
Air line (approximately)
289 kilometers
156 nautical miles