The smallest that I make these car seat cover uppers is 30" x 38". The last one I made was 34" x 42". It really depends on how much fabric I have. I usually put cotton on the front and flannel on the back and a lightweight batting as I don't want it too heavy. I just quilt it with my machine and machine bind it like a regular little quilt. My straps are usually about 10" after seaming ready for velcro and I sew them directly on the quilt with a couple of rows of machine stitching right in the centre of the strap. Hope this helps.
P.S. I checked out the tutorial link provided by Yakkity and this looks pretty well like mine except her straps are wider and she used fleece instead of cotton.
Last edited by Shelbie; 02-15-2014 at 02:18 PM.