I'm going to be doing my first grooms cake in October that is to be served at the reception. There are going to be approx. 150 people at the wedding. Do I make sure that the cake will serve 150 or no since there is obviously going to be a wedding cake as well (not done my me). Please let me know what you think. Thanks!

I've never made a groom's cake, but from what I've always thought is it's supposed to be enough to feed the wedding party. The main wedding cake is for the bulk of the guests. If I'm wrong, hopefully my post will give you a nice bump and some better answers. Good luck!

Who ordered the cake? How many servings did the person order? Is this a gift from you? Generally the groom's cake is smaller than the wedding cake.

Every time Ive made a groom's cake, its usually much smaller than the main wedding cake.
Last one I did was just a 10" round, 2 layer, iced in chocolate ganache and topped with chocolate dipped strawberries made to look like little tuxes.
The main cake was approx. 225 serv.
So, about 1/4 of the size perhaps?
But, def. ask the bride (or groom) =)