Fideris has an area, (as of the 2004/09 survey) of . Of this area, about 58.7% is used for agricultural purposes, while 28.8% is forested. Of the rest of the land, 3.1% is settled (buildings or roads) and 9.4% is unproductive land. In the 2004/09 survey a total of or about 1.3% of the total area was covered with buildings. Of the agricultural land, is fields and grasslands and consists of alpine grazing areas. Since 1985 the amount of agricultural land has decreased by . Over the same time period the amount of forested land has increased by . Rivers and lakes cover in the municipality.