Sarn has an area, , of . Of this area, 78.9% is used for agricultural purposes, while 15.1% is forested. Of the rest of the land, 3.2% is settled (buildings or roads) and the remainder (2.8%) is non-productive (rivers, glaciers or mountains). The municipality is located in the Thusis sub-district, of the Hinterrhein district. It consists of the
haufendorf (an irregular, unplanned and quite closely packed village, built around a central square) village of Sarn on the
Heinzenberg mountains. The municipalities of Portein, Präz, Sarn, and Tartar merged on 1 January 2010 into the municipality of Cazis. ==Demographics==