The calculated distance (air line) between Frankfurt am Main and Herk-de-Stad is approximately 165 miles respectively 265 kilometers.
By car or train, the actual journey to Herk-de-Stad is certainly longer, as only the direct route (as the crow flies) between Frankfurt am Main and Herk-de-Stad has been calculated here.
Air line (approximately)
265 kilometers
143 nautical miles