The calculated distance (air line) between Renens and La Chaux-de-Fonds is approximately 40 miles respectively 65 kilometers.
By car or train, the actual journey to La Chaux-de-Fonds is certainly longer, as only the direct route (as the crow flies) between Renens and La Chaux-de-Fonds has been calculated here.
Air line (approximately)
65 kilometers
35 nautical miles