The calculated distance (air line) between Pyŏksŏng-ŭp and Wŏnsan is approximately 127 miles respectively 205 kilometers.
By car or train, the actual journey to Wŏnsan is certainly longer, as only the direct route (as the crow flies) between Pyŏksŏng-ŭp and Wŏnsan has been calculated here.
Air line (approximately)
205 kilometers
111 nautical miles