Loch Roag surrounds Bernera, extending from Carloway to Gallan Head in Uig. It comprises East Loch Roag, to the east of Bernera and West Loch Roag to the west.

Within Loch Roag are numerous smaller islands: Berisay, Pabbay, Vuia Mor, Keava and Kearstay, amongst many others.

An arm of the loch, known as Little Loch Roag, extends southwards to Morsgail.