The reserve encompasses 5,520 km² in the states of Karnataka (1527.4 km²), Kerala (1455.4 km²), and Tamil Nadu (2537.6 km²). The Biosphere lies Between 11o 36' to 12o 00' N Latitude and 76o 00' to 77o 15' E Longitude. Central location:
The Mudumalai WL Sanctuary and National Park (321.1 km²), Wayanad Wildlife Sanctuary(344km²), Bandipur National Park(874km²), Nagarhole National Park (643 km²), Nugu WLS, Mukurthi National Park (78 km²) and Silent Valley National Park (89.52km²) are protected areas within this reserve. The Bio-sphere Reserve also includes zones of The Nilgiris open to forestry and tourism including: Nilgiris District (North (448.3 km²) and Nilgiris District South (198.8 km²)), Erode District (Sathyamangalam forest (745.9km²) and Erode(49.3 km²)) and Coimbatore District (696.2 km²) in Tamil Nadu.
The reserve extends from the tropical moist forests of the windward western slopes of the Ghats to the tropical dry forests on the leeward east slopes. Rainfall ranges from 500 mm to 7000 mm per year. The reserve encompasses three ecoregions, the South Western Ghats moist deciduous forests, South Western Ghats montane rain forests, and South Deccan Plateau dry deciduous forests. The habitat types include montane rain forest, semi-evergreen moist forest, thorn forest and scrub, montane grassland, and high-elevation Shola forests.