The calculated distance (air line) between Nova Gradiška and Kotor Varoš is approximately 44 miles respectively 71 kilometers.
By car or train, the actual journey to Kotor Varoš is certainly longer, as only the direct route (as the crow flies) between Nova Gradiška and Kotor Varoš has been calculated here.
Air line (approximately)
71 kilometers
38 nautical miles