It is bounded on the north and west by the Minahassa Peninsula, and on the south by the East Peninsula. To the east it is open to the Molucca Sea.
The Togian Islands sit near the centre of the gulf.
The International Hydrographic Organization (IHO) defines the Gulf of Tomini as being one of the waters of the East Indian Archipelago. The IHO defines its eastern limit as "The Western limit of Molukka Sea [sic]", which is defined as "Tg. Pasir Pandjang ( ) and across to Tg. Tombalilatoe (123°21'E) on the opposite coast".