The calculated distance (air line) between Zürich (Kreis 3) and Rapperswil is approximately 18 miles respectively 28 kilometers.
By car or train, the actual journey to Rapperswil is certainly longer, as only the direct route (as the crow flies) between Zürich (Kreis 3) and Rapperswil has been calculated here.
Air line (approximately)
28 kilometers
15 nautical miles