Size
To fit preemie(0-6 mos, 6-12 mos, toddler) (youth/ adult small, adult medium, adult large.  
Circumference: 12(14, 16, 18) (20, 22, 24) in / 30.5(35.5, 40.5, 46) (51, 56,61) cm.
Yarn
120(145, 160, 185) (200, 220, 240) yds / 110(135, 150, 170) (185, 205, 220) m of worsted weight yarn.
Needles
US 4 / 3.5 mm needles
Gauge
20 sts / 28 rounds = a 4x4 in / 10x10 cm swatch in stockinette in the round, blocked.