The calculated distance (air line) between Le Mont-sur-Lausanne and Biel/Bienne is approximately 49 miles respectively 80 kilometers.
By car or train, the actual journey to Biel/Bienne is certainly longer, as only the direct route (as the crow flies) between Le Mont-sur-Lausanne and Biel/Bienne has been calculated here.
Air line (approximately)
80 kilometers
43 nautical miles