The man in the photo, Mr. HelloYarn, has a 23” head, measured where the base of the hat sits. This allows 2” of negative ease for the hat, so that it doesn’t stretch out and get too loose after a bit of wear. I have, however, been very sure when knitting to leave nice, long floats when switching colors, which leaves the fabric with good stretch. If you are new to color knitting, be sure to spread the stitches on your right hand needle out before you make a stitch in a new color. This makes sure your floats are long enough (they should ideally hump out a little bit to allow the fabric to stretch).