The nation's main island, it is south of Hokkaido across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyushu across the Kanmon Strait. It is the seventh largest island, and the second most populous island in the world after Java in Indonesia.

The island is roughly 1,300 km long and ranges from 50 to 230 km wide, and its total area is 230,500 km², 61% of the total area of Japan. It is larger than the island of Great Britain, and slightly larger than the state of Minnesota. Honshu has 5,450 km of coastline.