The calculated distance (air line) between Châtillon-sur-Seine and Saint-Étienne is approximately 168 miles respectively 270 kilometers.
By car or train, the actual journey to Saint-Étienne is certainly longer, as only the direct route (as the crow flies) between Châtillon-sur-Seine and Saint-Étienne has been calculated here.
Air line (approximately)
270 kilometers
146 nautical miles