Oh you're seaming.. I've never made one like that I always do them in the round. Well if you double worsted yarn you get appx bulky weight.
This one is knit in the round, but the cast on would be about the same if you seam it. You might cast on a few extra for seaming and don't count those two stitches in any pattern or the decreases. The cast on for this one is 64.
http://kaitysfreepatterns.wordpress..../plain-ol-hat/