Calculating how many stitches are needed

I know this should be easy to figure out but for some reason, my mind isn’t working this morning! hee hee I want to make a simple hat using size 8 circular needles. The yarn I will be using is 16 stitches per 4 inches. How many stitches would I need to cast on for an adult hat?

Ok, I think I figured it out. For a head that is 21 inches I would cast on 84 stitches?

You might want to make it one set of decreases smaller than that. You usually make a hat a little smaller than the head so that it will fit nicely.

I second the idea of rounding down (to 80 stitches)

its easier to shape the crown if you start with a mutliple of 8…

(make it 82 (80 plus 2 stitches to be lost in seam) if you plan to knit it flat and seam)

It also depends on the stitch your using. I have to make swatches for every stitch pattern I use. They’re all completly different.