Kleinkahl lies in the region known as Bavarian Lower Main (Bayerischer Untermain) in the Mittelgebirge Spessart. The municipal territory is located at the northern border of the district of Aschaffenburg and at the border between Bavaria and Hesse. It lies in the Kahlgrund, the valley of the river Kahl, a tributary of the Main. At Kleinkahl, the Kleine Kahl flows into the Kahl.