The calculated distance (air line) between Harpenden and Stoke-on-Trent is approximately 113 miles respectively 181 kilometers.
By car or train, the actual journey to Stoke-on-Trent is certainly longer, as only the direct route (as the crow flies) between Harpenden and Stoke-on-Trent has been calculated here.
Air line (approximately)
181 kilometers
98 nautical miles