The calculated distance (air line) between Muang Xay and Vang Vieng is approximately 126 miles respectively 203 kilometers.
By car or train, the actual journey to Vang Vieng is certainly longer, as only the direct route (as the crow flies) between Muang Xay and Vang Vieng has been calculated here.
Air line (approximately)
203 kilometers
109 nautical miles