A 10" round 4" high serves 38. A 6" round 4" high servese 12 -- that's exactly 50. And 8" high 4" serves 24, so that might be better in case you want extras.
A 10" square 4" high servese 50 all by itself.
These are wedding cake sizes though.
Visit the Wilton web site. They'll have sizings there I would imagine.
HTH - S.
This is the chart I use... I use the wedding chart for 2" cakes (they figure on double layers) for figuring all of my pricing. These serving sizes are 1"x2"x4"
http://www.wilton.com/cake/cakeprep/baking/times/index.cfm
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