The calculated distance (air line) between Le Blanc-Mesnil and Cergy-Pontoise is approximately 19 miles respectively 30 kilometers.
By car or train, the actual journey to Cergy-Pontoise is certainly longer, as only the direct route (as the crow flies) between Le Blanc-Mesnil and Cergy-Pontoise has been calculated here.
Air line (approximately)
30 kilometers
16 nautical miles