gauge swatch, and start knitting away. It's just a scarf, right? Exact measurements aren't important.
Except when your pattern takes exactly two skeins of yarn and that's all you have.
I realized after I was a quarter of the way done that I was knitting just under a 3/4 of an inch for every inch I should be knitting. That doesn't seem like much, but that means I'm either knitting a very short scarf or I don't have nearly enough yarn. Since I don't want a super short scarf, I ordered two more skeins of yarn (although I should only need one more) and they arrived today. They're from a different dye lot but close enough that I don't think anyone will notice.
One skein got me to almost a third of the length I want. So I've started on the second skein and I'm just over a third now, as you can see.
At this rate it's going to be very fat in the middle. Hopefully with the super tight knitting I apparently do it will be warm.
Next time I make this I'll have to try larger needles to compensate for how tight I knit.