The calculated distance (air line) between Frankfurt am Main and Montignies-sur-Sambre is approximately 186 miles respectively 300 kilometers.
By car or train, the actual journey to Montignies-sur-Sambre is certainly longer, as only the direct route (as the crow flies) between Frankfurt am Main and Montignies-sur-Sambre has been calculated here.
Air line (approximately)
300 kilometers
162 nautical miles