The calculated distance (air line) between Ashgabat and Gonbad-e Kāvūs is approximately 183 miles respectively 294 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 Ashgabat and Gonbad-e Kāvūs has been calculated here.
Air line (approximately)
294 kilometers
159 nautical miles