When looking at a flat 2-dimensional picture, it's hard to tell because you don't know the diameter of each tier.  Most cakes, regardless of shape, can be scaled to feed as many as needed.  With that being said, I will ask you, "How many guests do you need to feed?"  Once we know the needed servings, I can design with the correct pan sizes to get the correct amount of serving. If the design is a tiered cake design and costing over $250, when we meet I will build your cake design for you.  Most people are visual and it helps to actually see a 3-dimensional view of your cake design.  Below are standard serving sizes, although my sheet cakes are taller in height once the cake is filled and iced.

Wedding Cake Serving
4x3x1

1/4 Sheet Cake
9x13x2

1/2 Sheet Cake
12x18x2