The calculated distance (air line) between Saint-Macaire-en-Mauges and Brest is approximately 184 miles respectively 297 kilometers.
By car or train, the actual journey to Brest is certainly longer, as only the direct route (as the crow flies) between Saint-Macaire-en-Mauges and Brest has been calculated here.
Air line (approximately)
297 kilometers
160 nautical miles