The calculated distance (air line) between Kaesŏng and Pyŏksŏng-ŭp is approximately 55 miles respectively 88 kilometers.
By car or train, the actual journey to Pyŏksŏng-ŭp is certainly longer, as only the direct route (as the crow flies) between Kaesŏng and Pyŏksŏng-ŭp has been calculated here.
Air line (approximately)
88 kilometers
47 nautical miles