What size yarn do you need to crochet a hat?
For both knit and crochet, the general rule of thumb is that a typical 100g skein of yarn will safely make you a hat. Crochet takes about 25% more yarn than knitting (though it depends a lot on the stitches used!). So if you knit it, you will have more left over than if you crochet.
Can I use blanket yarn for a hat?
“Blanket yarn us super bulky, super soft and super warm. It works up quickly and is very fun to use. Available in a variety of colors, quick working blanket yarn can make wonderful warm hats! … One skein of blanket yarn will make at least two hats.