Carstairs is a parish, which lies in South Lanarkshire Council Area, some 5 miles (8 km) east of Carluke and 13 miles (20 km) northeast of Douglas in South Lanarkshire.
It is located in the old county of Lanarkshire, which disappeared following the Local Government (Scotland) Act 1974.
The parish has an area of 40 sq. km (15.4 sq. miles). Carstairs has 6 neighbouring parishes; namely Cambusnethan, Carluke, Carnwath, Lanark, Pettinain and West Calder.