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