The calculated distance (air line) between Jämsänkoski and Seinäjoki is approximately 96 miles respectively 155 kilometers.
By car or train, the actual journey to Seinäjoki is certainly longer, as only the direct route (as the crow flies) between Jämsänkoski and Seinäjoki has been calculated here.
Air line (approximately)
155 kilometers
84 nautical miles