Beanie sizing

Hello. It’s been a lllooonnnggg time since I’ve knit a beanie. I used a pattern ages ago that I want to do again but can’t find it online. I’m pretty sure I can recreate it from memory. However, how do I determine how many stitches to start with. The rim will be a 2x2 knit with the main head piece being stockinette with a swirl that goes around. It will be knit in the round.

Should I measure my partners head and then see how many stitches per inch of chosen yarn and do it that way? Maybe make it a tad smaller since it will be a stretchy knit?