I found that most websites and people all had different opinions. In the end I found that the Warm and Natural or Warm and White quilt batting comes in precut sizes and I've decided to go with that. My advice would be to make the quilt about 1" smaller than the batting to take care of any stretching or warping of the batting and backing when you quilt as I have seen most places agree you should have a larger backing than quilt top when quilting.
Here are the sizes that I recorded.
http://www.costumewardrobe.com/2009/...d-quilt-sizes/
Use those measurements on your bed to see if it will be the size you want or if you want to make yours a little smaller.