The calculated distance (air line) between Brest and Perros-Guirec is approximately 56 miles respectively 90 kilometers.
By car or train, the actual journey to Perros-Guirec is certainly longer, as only the direct route (as the crow flies) between Brest and Perros-Guirec has been calculated here.
Air line (approximately)
90 kilometers
49 nautical miles