Size 1 Template (about 3-4.5lbs) and Size 2 Template (about 4-6lbs)... all depending on girth, development, and build...
A fitted made from the size 1 template from stretchy fabrics like interlock, knit, bamboo or cotton fleece, or T-shirts is actually a size 2 (approx. 4-6lbs), and a PUL FOE cover for it should be made from the size 2 template. For smaller preemies (too small to be brought home and most NICUs won't use home-made CDs), make a cover from the size 1 (with the foldable dip and not the snap-down) template and sew lay-in contour pads/soakers using the inner soaker shape of the template. :)
Here is a size 1 PUL pocket diaper next to my XS pocket AIO (which is a pretty typical newborn sized AIO).
Size 1 front pocket diaper (stuffed with a rectangular insert) with 1/4" elastic.