The calculated distance (air line) between Serang and Rengasdengklok is approximately 79 miles respectively 127 kilometers.
By car or train, the actual journey to Rengasdengklok is certainly longer, as only the direct route (as the crow flies) between Serang and Rengasdengklok has been calculated here.
Air line (approximately)
127 kilometers
68 nautical miles