The calculated distance (air line) between San Martino Buon Albergo and Prato is approximately 106 miles respectively 171 kilometers.
By car or train, the actual journey to Prato is certainly longer, as only the direct route (as the crow flies) between San Martino Buon Albergo and Prato has been calculated here.
Air line (approximately)
171 kilometers
92 nautical miles