Hernani is a town and municipality situated in the province of Gipuzkoa within the Basque Autonomous Community of Spain. It is positioned on the left bank of the Urumea river.
The municipality covers an area of approximately 40 square kilometres. It is located 9.2 km from the city of San Sebastián and shares borders with the neighboring municipalities of Astigarraga, Arano, Elduayen, Errenteria, Lasarte-Oria, and Urnieta.