The island of Ummanz lies in the Baltic Sea, off the west coast of the island of Rügen, and belongs, like the latter, to the county of Vorpommern-Rügen in the German state of Mecklenburg-Western Pomerania.

It is part of the Western Pomerania Lagoon Area National Park.

The island is bounded to the west and northwest by the Schaproder Bodden, to the north, by the inlet of Udarser Wiek, to the east by the lake of Koselower See and the Breite and to the south by the Kubitzer Bodden.

The island of Ummanz is very flat; its highest point lying just 3 metres above sea level (NN).

As a result, Stralsund's citizens exercised lordship over the island for centuries on behalf of the church foundation.