Measurements
To fit average head size
56 cm (22 inches)

The given length of yarn is for the whole hat set:
Hat, Gloves and Knotted Scarf.

Each pamphlet has a different set of recommended yarns. The following are from the Studley version.

Materials
For full set
Hat, Gloves and Scarf
STUDLEY Double Knitting
Five-in-One
4 balls
Five-in-One Royal
4 balls
Five-in-One Fashion
4 balls.