Quiltler's size guide uses 36 by 52 inches for a baby or crib quilt. Add 4 inches of overhang on every side and the back is 44 by 60. That 44 inch width is just past a typical 42 inch usable bolt, so two panels of standard cotton is the honest answer — not “one yard of backing.” Change the numbers in the card if your crib quilt is a receiving blanket at 30 by 40, or a toddler quilt at 40 by 60.
Why a baby quilt still seams
People expect crib backs to be a single panel. The math disagrees unless you buy wide cloth or a Minkee-style backing sold extra wide. Two 42 inch panels seamed along the 60 inch side is a quiet join under a small quilt. Press the seam open, and keep it off the centre of a pieced top if the quilting will outline a medallion.
Binding and batting for the same 36 by 52 size sit on how much fabric for a baby quilt and how much binding for a baby quilt. Design the gift in the baby quilt designer when the top is pieced, not a rectangle. Seaming method is how to piece quilt backing. Width-of-fabric language is quilt width of fabric.