Yarn tricks:
#1. To add more yarn when you run out, keep 5 inches of the yarn you were using, lay 5 inches of new yarn with it, then, using the yarn you are running out of, continue to crochet new stitch, but pick up the new yarn to pull through final 2 loops on hook.
#2. If using wool yarn in above scenario, wet about 3 inches of both ends of yarn and roll through your fingers. This will ''felt' the yarns together.

Crochet Counting Measurements Rather Than Stitches
 This is the original pattern using a worsted weight yarn in wool
 Same pattern using bulky yarn in wool, but left out the twist
This one will have fewer rounds and fewer stitches
 Same pattern using a sport weight yarn in wool
I have more stitches per round and more rounds
Here I used a smaller yarn in cashmere
Wow. Many many rounds in this one.

However, all of the hats would start the twist at 3" and the diameter of the crown would be 8". The total length of the hats would all be 8" as well and all of the hats will fit the same size head.