Chomutov District borders Germany in the north. The district consists of two distinct parts, the forested and mountainous landscape in the northwest and the flat, mainly agricultural landscape in the southeast. The territory extends into three geomorphological mesoregions: Most Basin (south and east), Ore Mountains (north and west), and Doupov Mountains (small part in the southwest). The highest point of the district and the entire Ústí nad Labem Region is a contour line below the top of the Klínovec Mountain in Loučná pod Klínovcem with an elevation of 1,231 metres (4,039 ft), the highest peak is the nearby Macecha at 1,113 m (3,652 ft). The lowest point is the river bed of the Ohře in Březno at 220 m (720 ft).
From the total district area of 935.7 km2 (361.3 sq mi), agricultural land occupies 387.9 km2 (149.8 sq mi), forests occupy 360.3 km2 (139.1 sq mi), and water area occupies 31.0 km2 (12.0 sq mi). Forests cover 38.5% of the district's area.[1]
The most important river is the Ohře, which flows across the southern part of the territory. Notable are the rivers Bílina and Chomutovka that originates here and drain the northern part. The largest bodies of water are the reservoirs Nechranice (the sixth largest reservoir in the country) and Přísečnice. There are also several ponds and the artificial lake Kamencové jezero.