The calculated distance (air line) between Dien Bien Phu and Luang Prabang is approximately 118 miles respectively 189 kilometers.
By car or train, the actual journey to Luang Prabang is certainly longer, as only the direct route (as the crow flies) between Dien Bien Phu and Luang Prabang has been calculated here.
Air line (approximately)
189 kilometers
102 nautical miles