The calculated distance (air line) between Balsthal and Zürich (Kreis 11) is approximately 39 miles respectively 64 kilometers.
By car or train, the actual journey to Zürich (Kreis 11) is certainly longer, as only the direct route (as the crow flies) between Balsthal and Zürich (Kreis 11) has been calculated here.
Air line (approximately)
64 kilometers
34 nautical miles