The calculated distance (air line) between Mendig and Höhr-Grenzhausen is approximately 18 miles respectively 28 kilometers.
By car or train, the actual journey to Höhr-Grenzhausen is certainly longer, as only the direct route (as the crow flies) between Mendig and Höhr-Grenzhausen has been calculated here.
Air line (approximately)
28 kilometers
15 nautical miles