Hengyang is located in the central-southern part of Hunan Province, in the middle reaches of the Xiang River, south of Mountain Heng.

It is situated between 110^o32′16″ E and 113^o16′32″ E, and between 26^o07′05″ N and 27^o28′24″ N. To the east, it borders You County of Zhuzhou City; to the south, it adjoins Anren County, Yongxing County, and Guiyang County of Chenzhou City; to the west, it neighbors Lengshuitan District and Qiyang County of Yongzhou City, as well as Shaodong County of Shaoyang City; to the north, it is adjacent to Shuangfeng County of Loudi City and Xiangtan County of Xiangtan City. The city stretches 150 kilometers from north to south and 173 kilometers from east to west.

The total area of Hengyang is 15,310 square kilometers.