The area of the district is 378 hectares. Thereof fall 54.2% upon agriculturally used area, 34.7% upon forest area, 7.9% upon settlement area and roads, 1.9% upon water expanse and 1.3% upon other.
Obernau has a population of 503 people and is therefore the second smallest district of Rottenburg. At an area of 3.78 km² this corresponds to a population density of 133 people per km², or 345 per sq mi.