The calculated distance (air line) between Idrija and Šempeter pri Gorici is approximately 19 miles respectively 31 kilometers.
By car or train, the actual journey to Šempeter pri Gorici is certainly longer, as only the direct route (as the crow flies) between Idrija and Šempeter pri Gorici has been calculated here.
Air line (approximately)
31 kilometers
17 nautical miles