The calculated distance (air line) between Belogradchik and Stara Zagora is approximately 171 miles respectively 275 kilometers.
By car or train, the actual journey to Stara Zagora is certainly longer, as only the direct route (as the crow flies) between Belogradchik and Stara Zagora has been calculated here.
Air line (approximately)
275 kilometers
148 nautical miles