The calculated distance (air line) between Chiang Saen and Chiang Rai is approximately 30 miles respectively 49 kilometers.
By car or train, the actual journey to Chiang Rai is certainly longer, as only the direct route (as the crow flies) between Chiang Saen and Chiang Rai has been calculated here.
Air line (approximately)
49 kilometers
26 nautical miles