The number of dowels needed for a 12-inch cake depends on the weight of the cake that will be placed on top of it. However, as a general guideline, for a 12-inch cake supporting a lighter cake, you might need around 5 dowels. If the cake on top is heavier, you might need to use more dowels, up to 8 or more, to ensure stability. It's crucial to remember that the dowels must be evenly spaced to distribute the weight properly. For the best results, it's always recommended to consult with a professional cake decorator or baker.