This is the standard batting size.  I make my quilts as close to the size of the batting as possible.

Crib Quilt	45" x 60"
Twin Quilt	72" x 90"
Double Quilt	81" x 96"
Queen Quilt	90" x 108"
King Quilt	120" x 120"

This is the standard mattress size.  I use these measurements to determine how large I want my bedspreads to be.

Start with the mattress size and decide how much you want to tuck under the pillow (double that measurement).  Remember it is going under the pillow and back out again.  Then decide if it is going to go to the floor or where you want it to stop at on the sides and end of the bed.

Crib Quilt	27" x 50"
Twin Quilt	39" x 75"
Double Quilt	54" x 75"
Queen Quilt	60" x 80"
King Quilt	72" x 84"