The calculated distance (air line) between Gumdag and Gonbad-e Kāvūs is approximately 139 miles respectively 223 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 Gumdag and Gonbad-e Kāvūs has been calculated here.
Air line (approximately)
223 kilometers
120 nautical miles