Birrhard has an area, , of . Of this area, or 52.8% is used for agricultural purposes, while or 33.8% is forested. Of the rest of the land, or 12.4% is settled (buildings or roads), or 1.7% is either rivers or lakes. Of the built up area, industrial buildings made up 0.7% of the total area while housing and buildings made up 6.0% and transportation infrastructure made up 4.7%.. 32.8% of the total land area was heavily forested. Of the agricultural land, 46.2% is used for growing crops and 5.7% is pastures. All the water in the municipality is in rivers and streams.