The calculated distance (air line) between Portes-lès-Valence and Saint-Étienne is approximately 45 miles respectively 73 kilometers.
By car or train, the actual journey to Saint-Étienne is certainly longer, as only the direct route (as the crow flies) between Portes-lès-Valence and Saint-Étienne has been calculated here.
Air line (approximately)
73 kilometers
39 nautical miles