T-Shirt Quilts

[putontheritz.livejournal.com]

Okay craftgrrls (and guys?)

I am not a sewer or a quilter. However, I'm getting married, and as something I'd like to do before I get married, I want to make a t-shirt quilt with my mother (who has more sewing experience than I).  I've checked some of the memories and haven't really found anything.  I've looked at some online websites, and couldn't really find specific answers to the questions I'm looking for.

I currently have 50 t-shirts.  I would like to do a quilt with 25 on each side, 5 rows of 5.  I've found that the standard "square" size once it's sewn is 15 inches, which sounds about right to me. 

I found a website that says, whatever I want the t-shirt size to be, I should make a cardboard square and use it as a stencil to each shirt, and that I should factor in a 2 and a half border, for sewing potential.  Is that right?  That would make my squares 17 and a half inches on all four sides, and I'm worried that some of them would be too small. Maybe I should aim for 14 inch squares? 

General opinions would be highly appreciated. Or any "better" websites on how to do this.  Maybe my google-fu isn't working great today. 

And considering that both sides will have t-shirts on them, how many yards of fabric do you think I'll need?