The calculated distance (air line) between Whangarei and Ngaruawahia is approximately 141 miles respectively 228 kilometers.
By car or train, the actual journey to Ngaruawahia is certainly longer, as only the direct route (as the crow flies) between Whangarei and Ngaruawahia has been calculated here.
Air line (approximately)
228 kilometers
123 nautical miles