I had a pattern to make a baby bib, which I did; it’s basically half of what you see here, except it has ties. For this I CO 49 sts, knitted 1 row and then knitted 19 sts, carried 1 stitch from left needle to right needle, put right needle through 2 sts as if to knit, then passed carried over stitch over those 2 sts. This makes a double decrease (DD). Then knit the remaining 19 sts. Knit next row back. Proceed in this way; next, knit 18 sts, do the DD and knit remaining 18 sts and knit the row back.
It ends up making a square. You can use whatever size knitting needle you wish.