The calculated distance (air line) between Luang Prabang and Xam Nua is approximately 128 miles respectively 206 kilometers.
By car or train, the actual journey to Xam Nua is certainly longer, as only the direct route (as the crow flies) between Luang Prabang and Xam Nua has been calculated here.
Air line (approximately)
206 kilometers
111 nautical miles