The post include stitch and row counts for 3 different yarn weights (sport, worsted, bulky). They all make a hat that is 19″ around and 11″ in length (with brim unfolded).

Hook sizes:
Sport - 5.5mm
Worsted - 6.5mm
Bulky - 10mm

The stitch is stretchy so it should fit most, but the hat can be easily made wider with additional short rows.