The calculated distance (air line) between Gonbad-e Kāvūs and Serdar is approximately 134 miles respectively 215 kilometers.
By car or train, the actual journey to Serdar is certainly longer, as only the direct route (as the crow flies) between Gonbad-e Kāvūs and Serdar has been calculated here.
Air line (approximately)
215 kilometers
116 nautical miles