Thorin's company includes 13 dwarves, counting Thorin himself. The group consists of Thorin Oakenshield and twelve companions: Fíli, Kíli, Dori, Nori, Ori, Óin, Glóin, Bifur, Bofur, Bombur, Balin, and Dwalin.
The company forms the central expedition in J. R. R. Tolkien's The Hobbit. Thorin leads them on a quest to reclaim Erebor, the Lonely Mountain, and its treasure from the dragon Smaug. Gandalf brings Bilbo Baggins into the adventure as the company's burglar, so Bilbo is an additional member of the travelling party but not one of the thirteen dwarves.
A common mix-up comes from counting only Thorin's twelve companions and answering 12. The wording “including Thorin” is important: twelve dwarves accompany their leader, producing a total of thirteen. Gandalf also travels with the group for parts of the journey, but he is a wizard, not a dwarf. Tolkien drew many of the dwarves' names from the Old Norse poem Völuspá.