The calculated distance (air line) between Donostia / San Sebastián and Ustaritz is approximately 27 miles respectively 43 kilometers.
By car or train, the actual journey to Ustaritz is certainly longer, as only the direct route (as the crow flies) between Donostia / San Sebastián and Ustaritz has been calculated here.
Air line (approximately)
43 kilometers
23 nautical miles