The calculated distance (air line) between Thimphu and Samdrup Jongkhar is approximately 123 miles respectively 199 kilometers.
By car or train, the actual journey to Samdrup Jongkhar is certainly longer, as only the direct route (as the crow flies) between Thimphu and Samdrup Jongkhar has been calculated here.
Air line (approximately)
199 kilometers
107 nautical miles