I have no idea how to even word this for a proper Google search, but the bottom line is that my wife is launching an online store tomorrow to make and sell matching bandanas and scrunchies for dogs and their owner. What we are looking for is an online tool where we can input the dimensions of her fabric, and the different sizes of rectangles she is using, to figure out how to maximize the fabric to the amount of bandanas and scrunchies she can make.

I've crudely done some napkin sketches for her, but not all fabrics are the same size and she made need more of one size and less of another, which would need her to rearrange all the shapes. I'm looking for a website or program that we can easily visualize this on. I know one has to exist, I just can't think of how to properly search for one. 

Extremely specific and odd topic, I know, but figured it was worth a shot?

Here are a couple options. An app Cut List Optimized may work. I use it for plywood and dimensional  lumber to optimize yield. 

 You may also want to try Sketch Up which would be manual. You would have to figure out the correct cutting pattern but it's easier than a napkin.