I am doing my first wedding cake for a friend of my sister. The bride says she will have 200-250 guests but that not all will eat cake. She is asking how many servings I think she really needs. I have NO IDEA - anyone out there who can guide me on this?

If she isn't sure an exact amount I would have at least 225 servings. Are they having a grooms cake? That could help you decide.

Y'know I mean you can give her a guide like this.
I just googled How many guests will attend?
And there were several like this.

http://www.websitetoolbox.com/tool/post/wedding_planning/vpost?id=162680

But be firm about the bride making that decision.
It's not your call.
It's your responsibility to make an adequate amount of cake.
It's her responsibility to order and pay for what she orders.

It's not your responsibility because then she can corner you
for any serving issues later. I mean if they cut the cake twice as
big as they are supposed to cut it then that's all under her purview
not yours. Or if they cut it small or if they have 100 fewer guests due
to weather and there's beaucoups of leftover none of those issues are your responsibility. It's all her responsibility.

She buys cake to serve x amount. You make it. That's all. It's her party.

Not to mention the number of guests that will say, "WOW, this cake tastes great!! I need two more pieces." That would be me.

I have seen a forum that indydebi had posted in about this very thing. I can't remember what the forum was. I think she said her rule of thumb was 60% of the guest list or invitation list. Maybe she could give her in put on this. She is a wealth of knowledge.

Thanks for the input! I think she just doesn't want to be stuck with a bunch of cake left over. She doesn't really eat cake herself and is only having a cake because it is expected, not because she wants one.

I used the calculator that k8memphis found with 200 and 250 guests and got a range of 152 - 190. So I think I will tell her we should provide for at least 200 and let her know that if she okays that number, she'll have to deal with unhappy guests if more show up and all of them want cake!