The calculated distance (air line) between Saint-Quentin-en-Yvelines and Blois is approximately 87 miles respectively 141 kilometers.
By car or train, the actual journey to Blois is certainly longer, as only the direct route (as the crow flies) between Saint-Quentin-en-Yvelines and Blois has been calculated here.
Air line (approximately)
141 kilometers
76 nautical miles