The calculated distance (air line) between Harrow on the Hill and Abbots Langley is approximately 10 miles respectively 16 kilometers.
By car or train, the actual journey to Abbots Langley is certainly longer, as only the direct route (as the crow flies) between Harrow on the Hill and Abbots Langley has been calculated here.
Air line (approximately)
16 kilometers
9 nautical miles