The calculated distance (air line) between Sha Tau Kok and Tuen Mun is approximately 19 miles respectively 31 kilometers.
By car or train, the actual journey to Tuen Mun is certainly longer, as only the direct route (as the crow flies) between Sha Tau Kok and Tuen Mun has been calculated here.
Air line (approximately)
31 kilometers
17 nautical miles