Great reference for hat sizes! - Hat sizing chart Age (Diameter of circle) Newborn in) months in) months in) Toddler/Sm Child Adult Woman Age (Finished Length) Newborn months Toddler/Sm Child Adult Large Adult
5 Helpful Crochet Size Charts from Starting Chain - includes links to hat sizing chart, blanket sizing chart, mitten pattern, baby clothes sizing chart, and baby bootie sizing chart. I have been looking for a hat sizing chart.
Basic DC Circle Pattern - The double crochet hat pattern has been around for eons. It is also a standard mandala pattern as well. Once you hit the circumference in increases then just do rounds of dc in each stitch for a deep as you want the hat.