It is slightly smaller than Peru and slightly larger than South Africa. Chad is in north central Africa, lying between latitudes 7° and 24°N, and 13° and 24°E. Chad is bounded to the north by Libya, to the east by Sudan, to the west by Niger, Nigeria and Cameroon, and to the south by the Central African Republic. The country's capital is 1,060 kilometres (660 mi) from the nearest seaport Douala (Cameroon). Due to this distance from the sea and the country's largely desert climate, Chad is sometimes referred to as the "Dead Heart of Africa".

A heritage of the colonial era, Chad's borders do not coincide wholly with natural boundaries. The dominant physical structure is a wide basin bounded to the north, east and south by mountain ranges such as the Ennedi Plateau in the north-east. Lake Chad, after which the country is named, is the remains of an immense lake that occupied 330,000 square kilometres (130,000 sq mi) of the Chad Basin 7,000 years ago.

Although in the 21st century it covers only 17,806 square kilometres (6,875 sq mi), and its surface area is subject to heavy seasonal fluctuations, the lake is Africa's second largest wetland. The Emi Koussi, a dormant volcano in the Tibesti Mountains that reaches 3,414 metres (11,201 ft) above sea level, is the highest point in Chad and the Sahara.

The region's tall grasses and extensive marshes make it favourable for birds, reptiles, and large mammals. Chad's major rivers—the Chari, Logone and their tributaries—flow through the southern savannas from the southeast into Lake Chad.