That of course depends on how tall and how rich (fatty) the cake is. If it's a light sponge like a génoise it will serve less people. In Europe.
G Grooms Servings (using the top tier). H Pan Sizes in Round layer tiers only. 5 inch, 16 inches, 6, 20, 35, 40, 11 - 5. 6 inch, 19 inches, 8, 25, 40, 50, 12 -6. 7 inch.
What size cake do I need? Here is our cake servings chart and servings per cake guidelines. 3 tier wedding cakes start at 10 pounds (50 servings) using 6", 9", & 12 " tiers. 4 tier wedding cakes (Size in inches is for reference) (Plain, Marble. Wilton Cake Baking and Serving Guide. The charts below are based on baking recommendations from the Wilton Test Kitchen; your results may vary depending.
NEW Round Cake Serving Guide/Chart - There is a similar graph to this on Cake Central, but it is not very large, Based on 1x2 inch servings, If you would like.
When estimating the size of the wedding cake assume the serving size will at least be that big and then figure out 12 Inch, 105, 139, 120.