The calculated distance (air line) between Üsküdar and Büyükçekmece is approximately 22 miles respectively 36 kilometers.
By car or train, the actual journey to Büyükçekmece is certainly longer, as only the direct route (as the crow flies) between Üsküdar and Büyükçekmece has been calculated here.
Air line (approximately)
36 kilometers
19 nautical miles