The calculated distance (air line) between Gonbad-e Kāvūs and Gumdag is approximately 139 miles respectively 223 kilometers.
By car or train, the actual journey to Gumdag is certainly longer, as only the direct route (as the crow flies) between Gonbad-e Kāvūs and Gumdag has been calculated here.
Air line (approximately)
223 kilometers
120 nautical miles