The calculated distance (air line) between Chalfont St Giles and Southend-on-Sea is approximately 56 miles respectively 89 kilometers.
By car or train, the actual journey to Southend-on-Sea is certainly longer, as only the direct route (as the crow flies) between Chalfont St Giles and Southend-on-Sea has been calculated here.
Air line (approximately)
89 kilometers
48 nautical miles