I cast on 70 sts for the smallest size - came out 16-1/2” - pretty big for a little baby. Next time I’ll cast on fewer sts. Worked up fast and easy. I made this for a charity drive - Little Hats, Big Hearts - that ran from Sept 1 thru Sept 30, 2014.

1st hat - 70 st on size 7 = 16.5” diam
2nd hat - 60 st on size 7 = 14” diam

All of the crocheted hats are similar - starting from the top/middle, then increasing in each round until long enough. I added some different edgings to some of them.