The calculated distance (air line) between Si Racha and Phra Nakhon Si Ayutthaya is approximately 85 miles respectively 136 kilometers.
By car or train, the actual journey to Phra Nakhon Si Ayutthaya is certainly longer, as only the direct route (as the crow flies) between Si Racha and Phra Nakhon Si Ayutthaya has been calculated here.
Air line (approximately)
136 kilometers
74 nautical miles