The calculated distance (air line) between Ermont and Paris 15 Vaugirard is approximately 10 miles respectively 17 kilometers.
By car or train, the actual journey to Paris 15 Vaugirard is certainly longer, as only the direct route (as the crow flies) between Ermont and Paris 15 Vaugirard has been calculated here.
Air line (approximately)
17 kilometers
9 nautical miles