The calculated distance (air line) between Abercynon and Southend-on-Sea is approximately 174 miles respectively 279 kilometers.
By car or train, the actual journey to Southend-on-Sea is certainly longer, as only the direct route (as the crow flies) between Abercynon and Southend-on-Sea has been calculated here.
Air line (approximately)
279 kilometers
151 nautical miles