It is not possible to determine the diameter of a cake based solely on its weight (250 g). The size of a cake can vary widely depending on its recipe, shape, and height.
The weight of a cake is not directly proportional to its diameter. Different cake recipes and baking techniques can yield cakes with varying densities, heights, and diameters, even if they weigh the same.
To determine the diameter of a cake, you would need to refer to a specific recipe and follow the instructions on baking pan size and filling level. The recipe should provide guidance on the appropriate pan size and how much batter to use, which will ultimately determine the cake's diameter.
Keep in mind that the height and diameter of the cake may change slightly during the baking process due to rising and settling. Baking is a science, and the outcome can be influenced by several factors, so it's essential to follow the recipe carefully for the best results.