Pattern gives directions for the following sizes:

Wee Noggin - 17.5”/45 cm circumference,

7.75”/20 cm brim-to-top

Normal Noggin - 22”/56 cm circumference,
9”/23 cm brim-to-top

Big Noggin - 26.5”/67 cm circumference,
10.25”/26 cm brim-to-top