Rhu is a coastal parish, which lies in Argyll and Bute Council Area, some 8 miles (13 km) north of Greenock in Inverclyde and 9 miles (15 km) northwest of Alexandria in West Dunbartonshire.
It is located in the old county of Dunbartonshire, which disappeared following the Local Government (Scotland) Act 1974.
The parish has an area of 82.5 sq. km (31.8 sq. miles) and includes the settlement of Helensburgh. Rhu has Cardross, Luss and Rosneath as its neighbouring parishes.