The calculated distance (air line) between Saint-Quentin-en-Yvelines and Poitiers is approximately 170 miles respectively 274 kilometers.
By car or train, the actual journey to Poitiers is certainly longer, as only the direct route (as the crow flies) between Saint-Quentin-en-Yvelines and Poitiers has been calculated here.
Air line (approximately)
274 kilometers
148 nautical miles