The calculated distance (air line) between Agra and Fatehpur Sīkri is approximately 23 miles respectively 37 kilometers.
By car or train, the actual journey to Fatehpur Sīkri is certainly longer, as only the direct route (as the crow flies) between Agra and Fatehpur Sīkri has been calculated here.
Air line (approximately)
37 kilometers
20 nautical miles