Rassau lies to the west of Beaufort in the county of Blaenau Gwent, South Wales. It is bordered by Sirhowy and Ebbw Vale to the south, Tafarnaubach to the west, Garnlydan to the east and Cefn Onnau to the north. Locals refer to either Old Rassau and New Rassau or Bottom Rassau and Top Rassau. The valleys towns and villages of Tredegar, Rhymney, Llechryd, Merthyr Tydfil, Cwm, Abertillery, Ebbw Vale, Markahm, New Tredegar, Bargoed, Blackwood and Newbridge all lie nearby.