It is in the form of a shallow crescent, some 4 miles or 6 km across, between St Ives in the west and Godrevy Head in the east.
At the most southerly point of St Ives Bay, the River Hayle flows into the sea through sand dunes and across the beach.
Behind the dunes, the river forms a broad tidal estuary which includes an area of salt marsh and a largely disused port (see article on the industrial history of Hayle).
The estuary is a popular place for birdwatching and the Royal Society for the Protection of Birds maintains a reserve there.
The eastern coast of the bay is a three-mile (5 km) unbroken sandy beach backed by a substantial system of coastal dunes known as The Towans which stretches from Porth Kidney Sands in the west to Godrevy Head in the east.