Turns out the blanket is about a half yard shorter than what I need. For the record it's a yard and a half of 66" wide fabric. Two yards will do nicely.
THEN I remembered that I wanted this jacket way shorter anyway. I want it to be a comfortable wear while sitting down. I figured about 9" off the bottom and, turns out, the blanket has enough fabric after all! I may have to make the collar/cowl out of something else.
And wow does unedged fleece shed. Yikes.