Tessagin, your boxes are gorgeous!
Here are the ones I made with French Seams.
http://www.quiltingboard.com/tutoria...l-t235889.html
Two factors determine the final size of your boxes: the size of the square you begin with and the size/depth of the corners you sew. In other words if you begin with a 15" square and make your corners a depth of 3" it will differ in size height and width from a 15" square where you make your corners a depth of 1.5".
You have to begin with one size square and play around until you come up with the combo you want. Some have made these boxes so you can put a roll of t.p. in them. I haven't made that size yet so I don't have the dimensions. I think the sky is the limit as to what you can fill them with.