Baby hat

I am still a newbie in knitting only have been knitting for a year. I have made several baby coocoons but now i am making a hat for the baby and need some help as to how long do I make the hat. The cocoons I was making them 21 to 26 inches long. I know that I don’t need it to be that long. What would be a good length for the hat. Thanks for all the help.

Here are some measurements for heights of baby hats depending on age and size that may help.

Probably begin the decreases at about 4-5", that should be okay.