Ainis is located in the upper Spercheios valley, bordering with Dolopia in the west, Oita in the south, Malis in the east and Achaia Phthiotis in the north. The exact borders with Oita and Malis have never been established. The river Spercheios floats through the region on its way down to the Maliac Gulf, and is joined in Ainis by its chief tributary the Inachos. The area is limited to the north by the Othrys mountains, and to the west by a spur of the Pindus mountains, with the peak of Tymphrestus visible from most of the region. To the south lies the peaks of Goulinas and Mount Oeta, separated by the river Inachus.