A classic 24 cm (about 9.5 inches) round cake tin typically yields between 12 and 16 decent, standard dessert servings when sliced into traditional triangular wedges.
If you are looking for generous, coffee-shop style slices where everyone gets a hearty piece, cutting the cake into 12 equal portions is the gold standard. Each slice will be substantial, satisfying, and hold its structure nicely without feeling skimpy.
If the cake is particularly rich, layered with heavy buttercream, or served directly after a large dinner, you can comfortably stretch it to 14 or 16 slices. To ensure clean, even slices without crushing the crumb, I always recommend dipping a sharp chef's knife in hot water and wiping it dry between each cut.
In short, planning for 12 generous portions or up to 16 standard slices is a reliable guideline for a 24 cm tin.