Using measurements rather than counting 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.