The calculated distance (air line) between Kowloon Tong and Tuen Mun is approximately 14 miles respectively 22 kilometers.
By car or train, the actual journey to Tuen Mun is certainly longer, as only the direct route (as the crow flies) between Kowloon Tong and Tuen Mun has been calculated here.
Air line (approximately)
22 kilometers
12 nautical miles