I guess it depends on the yarn and your preference. If you double the yarn, I'm not sure what size needle you would want to use; I just sort of guessed for mine!
Fear the Sock Monster! RAWR!
The individual has always had to struggle to keep from being overwhelmed by the tribe. If you try it, you will be lonely often, and sometimes frightened. But no price is too high to pay for the privilege of owning yourself. ~Friedrich Nietzsche Double Pointed - a knitting blog
Generally, the standard guideline is that if you double the yarn, double your needle size. Obviously it would be hard to find a size 21 needle... but the yarn you're using is probably bulky enough that you shouldn't need to double it.... If you want it to knit up faster, say on 15's, why not get a smooth worsted (or smaller) weight baby yarn to carry with it?? If your yarn is blue or pink, a strand of white mixed in would give it a great look...
As it stands right now, in the gauge you're knitting in, you would want to cast on 144 st for a 36in blanket.
Oh thank you for the info I was wondering how many stitches I was going to need. I like the idea of adding another color into it. That would add a bit of contrast to it. Thank you again everyone for all your help in this project!!
Cate, the blanket looks great!! I dont think the size will be a problem... the crib, the stroller, the carrier in the car, while walking... there are so many times when a baby needs a blanket... There is nothing better than a handmade gift...