The calculated distance (air line) between Chalfont Saint Peter and Hemel Hempstead is approximately 11 miles respectively 18 kilometers.
By car or train, the actual journey to Hemel Hempstead is certainly longer, as only the direct route (as the crow flies) between Chalfont Saint Peter and Hemel Hempstead has been calculated here.
Air line (approximately)
18 kilometers
10 nautical miles