Rockall is a very small island lying approximately 300 km (186 miles) west of St Kilda. St Kilda is 66 km (41 miles) west of Benbecula in the Outer Hebrides, and 430km (267 miles) from the nearest point on the Irish mainland. The outcrop measures circa 25m (82ft)* on its north-south axis and 22m (72ft)* on its east-west axis; the summit height was confirmed by Nick Hancock's 2014 GNSS survey as 17.15 metres above mean sea level, having been officially 19.2m (63ft) ASL prior to the summit being removed in 1971. It is situated on the Rockall Bank, an Atlantic ridge separated from the European continental shelf by the Rockall Trough.

The island is the core of an eroded volcano that erupted around 55 million years ago. The UKHO has confirmed that Rockall was positioned by Doppler survey in 1977 at 57 35.7781N, 13 41.2371W. This position was reconfirmed by GNSS satellite survey in 2014. Since 1997, the UK has only claimed a 12 nautical mile territorial sea around Rockall, acknowledging that it is legally a "rock" under Article 121 of the United Nations Convention on the Law of the Sea (UNCLOS). The UK's fishery zone off northwest Scotland is now measured from the westernmost tip of St Kilda. Although the UK's continental shelf extends across the Rockall Plateau, Rockall itself is not relevant to the definition of the continental shelf area, which is defined in UNCLOS as "the natural prolongation of [a state's] land territory to the outer edge of the continental margin". The main area of dispute is the Hatton Rockall basin, to the west of Rockall Island.

The occupiable area of Rockall, named in 1955 as Hall’s Ledge after the first recorded person to land there, is just 3.5 metres by 1.3 metres (11 foot by 4 foot), and is just obver 3 metres (10 foot) below the summit. There are no trees or bushes on the rock - just algae, moss, seaweeds and one black lichen. Just over 20 species of sea bird and only 6 species of animal have been recorded on or near Rockall. Greenpeace placed a solar powered beacon over the frame of the existing navigation aid in 1997, and returned to upgrade this light in 1998. This was the only permanent mark of human occupation on Rockall until it too succumbed to the ravages of an Atlantic storm two years later.

* These measurements have been averaged from the detailed maps available of Rockall at circa 1:100 scale. The differences in dimensions which have been recorded, from some of the most reputable UK mapping sources, is indicative of the divergence of knowledge still surrounding Rockall today.