The calculated distance (air line) between Zürich (Kreis 3) / Friesenberg 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) / Friesenberg and Rapperswil has been calculated here.
Air line (approximately)
28 kilometers
15 nautical miles