The calculated distance (air line) between Sabzevar and Gonbad-e Kāvūs is approximately 157 miles respectively 252 kilometers.
By car or train, the actual journey to Gonbad-e Kāvūs is certainly longer, as only the direct route (as the crow flies) between Sabzevar and Gonbad-e Kāvūs has been calculated here.
Air line (approximately)
252 kilometers
136 nautical miles