The calculated distance (air line) between Bojnūrd and Gonbad-e Kāvūs is approximately 120 miles respectively 193 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 Bojnūrd and Gonbad-e Kāvūs has been calculated here.
Air line (approximately)
193 kilometers
104 nautical miles