The island of Bali lies 3.2 km (2 mi) east of Java, and is approximately 8 degrees south of the equator. Bali and Java are separated by the Bali strait. From east to west, the island is approximately 153 km (95 mi) wide and spans approximately 112 km (69 mi) in width from north to south. Administratively it covers 5,780 km2, or 5,577 km2 not including Nusa Penida district. Its population density is roughly 750 people/km2.
Bali's central mountains include several peaks which are over 3,000 meters in height. The highest is mount Agung (3,031 m), known as the "Mother Mountain" which is an active volcano. Bali’s mountains range from the center of Bali to the eastern side of Bali, with mount Agung being the easternmost peak.
Bali's volcanic nature has contributed to its exceptional fertility and its tall mountain ranges provide the high rainfall that supports the highly productive agricultural sector. South of the mountains is a large descending area, where most of Bali's rice crop is grown. The northern side of the mountain slopes more steeply to the sea and is the main coffee producing area of the island, along with rice, vegetables and cattle. The longest river is Ayung and it flows approximately 75 km in distance.
The island is surrounded by coral reefs. The beaches in the south tend to have white sand, while those in the north and west have black sand. Bali has no major waterways, although the Ho river is navigable by small boats.
The largest city is Bali’s provincial capital, Denpasar, which is near the southern coast. Its population is around 500,000. Bali's second-largest city is the old colonial capital, Singaraja, which is located on the north coast and is home to around 100,000 people. Other important cities include the beach resort, Kuta, which is practically part of Denpasar's urban area, and Ubud, which is situated in the north of Denpasar and is the island's cultural centre.
There are three small islands that lie to the immediate south east and all are administratively part of the Klungkung regency of Bali. These are Nusa Penida, Nusa Lembongan and Nusa Ceningan. These islands are separated from Bali by the Badung strait.
To the east, the Lombok strait separates Bali from Lombok and marks the biogeographical division between the fauna of the Indomalayan ecozone and the distinctly different fauna of Australasia. The Strait is known as the Wallace Line, named after Alfred Russel Wallace, who was the first person to propose a transition zone between these two major biomes. When sea levels dropped during the Pleistocene ice age, Bali was connected to Java, Sumatra and to mainland Asia, so shared the Asian fauna. But Lombok island and the Lesser Sunda archipelago area were kept separated by the deep water of the Lombok strait.