The Solent coastline is around 241 miles long on the mainland between Selsey Bill and Hurst Spit, and includes Chichester, Langstone and Portsmouth Harbours, Southampton Water and the tidal extent of the main rivers. It is around 50 miles long from the Needles in the West to Bembridge in the East on the Isle of Wight. It is located at the southern margin of the Hamsphire Basin.
The stretch of sea itself is around 30 miles long and varies from 0.75 miles wide at its narrowest point to about 5 miles at its widest. It is considered to be the drowned valley of a river which once flowed east between what are now the Isle of Wight and the mainland of Hampshire and West Sussex.
It encompasses a major estuarine system with four coastal plain estuaries (Yar, Medina, King's Quay Shore, Hamble) and four bar-built estuaries (Newtown Harbour, Beaulieu, Langstone Harbour, Chichester Harbour). The Solent and its inlets are unique in Britain and Europe for their hydrographic regime of four tides each day, and for the complexity of the marine and estuarine habitats present within the area.
Parts of the coast are characterised by coastal accumulation forms such as barrier spits and islands, for example, Hurst and Calshot spits in the west Solent and Hayling Island in the east Solent. Erosional coastal environments are present along the coast of the Isle of Wight.
The offshore areas show complex morphology with several offshore banks and deeply incised channels like the Hurst Narrows.