I use this guide I find it a bit more generous than Wilton. It says a 10 inch square serves 40.
http://www.baking911.com/cakes/numberofservings_guide.htm
It depends on what you are giving as a serving. I use the party serving of 1.5"x2". By that serving size a 10" square would serve approx 30. An 8" would give you an additional 20 servings for a total of 50.
Not that I doubt you but the book I have says it feeds 24. . .
If you already knew then why did you ask?
And whats so hard about going to the Wilton website and looking at the chart?
I'm so confused as to why people ask questions like this.
Here is the chart 99% of cake bakers go by - 10" square cake - (2 - 10" layers) is 50 servings.
http://www.wilton.com/wedding/wedding-cakes/wedding-cake-data.cfm
She probably asked because there are so many different opinions on cake sizes and serving guides and a VERY wide range as well. It never hurts to ask the people that don't want to answer shouldn't.
I don't understand why some people on here have to be so nasty. If you can't say something nice don't say anything at all. It's really easy to hit the back button if something upsets you or you don't like the question. As for the cake servings I usually go by the Wilton Party cake chart. It's also going to depend on who cuts the cake and how big they think a slice should be. From my experience people don't think a 1x2 in slice is big enough. Just to be on the safe side I usually take the amount Wilton lists and cut it in half for party cakes. They tend to eat larger portions than someone at a wedding. Hope you find your answer. And by the way you didn't ask a stupid question.
I have that chart printed out and laminated so I can refer to it as needed! (and I keep a copy in my paperwork for tastings too) It is a valuable tool for those who make cakes.
Ditto
Cakeville: Maybe you should chill out and if you don't like my questions don't respond. It is people like you that make me very sad to know that my daughter has to grow up in a world that treats people like you do when it really didn't even have anything to do with you.
Everyone else who is helpful and productive, thank you VERY much! I really appreciate it.
This is why I give a range of number of servings. I think it is difficult for the average person to get the wilton wedding servings out of a round cake. I explain the difference in sizes and tell them how to cut the cake. Most people are still surprised you don't cut it into wedges!
I round the numbers and use that as a range.
). I used to be very confused as to which charts were best to use until I found this site.
This is why I give a range of number of servings. I think it is difficult for the average person to get the wilton wedding servings out of a round cake. I explain the difference in sizes and tell them how to cut the cake. Most people are still surprised you don't cut it into wedges!
I round the numbers and use that as a range.
It's very easy for anyone to get the wilton wedding servings out of a round cake if you give them a cutting chart like this http://www.cateritsimple.com/id10.html The wilton chart is pretty much the industry standard and if you're charging per serving that is the one I would use. If they want to cut bigger slices then they need to buy more cake.
I agree tiggy2, showing them Debi's diagram is VERY helpful because your average household has NO idea a party cake isn't cut into wedges when determing the serving size.
BTW, I'm all for people buying more cake to give me a decent slice. Those wedding pieces are merely a tease!! 
1x2x4 is actually a good size slice of cake.
I agree. I don't cut pieces of cake to serve at home any bigger than that.
I told you I must be greedy, LOL!!
I also don't bake for a living so cake is a treat around here, not a mainstay.
I am SICK of cake, icing and fondant.
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