Size 4 circular needle, mine is 16" from one tip to the other. Cast on 90.
K1P1 for 5 inches if you want a brim, 2.5 inches if you want a skull cap. I usually use two needles held together for the casting on so that the edge isn't really tight to the head.
Then place marker and switch to stockinette stitch for 4 inches. Then begin the decreases, *Knit 3 knit 2 together* repeat between ** to end of row. Then knit 2 rows in stockinette. Then *knit 2 knit 2 together* repeat between ** to end of row. Then knit 2 more rows in stockinette. At this point you may want to switch to double pointed needles size 4 still. Then *knit 1 knit 2 together* repeat between ** to end of row, knit 2 rows stockinette. Then knit 2 together all the way around, pick up the stitches with a sewing needle, draw it tight and knot it off.
I don't write patterns, so if I used the wrong symbols or something, I apologize. Enjoy!