Knitting Bolero Jacket

I am just learning to do knit Bolero Jacket for my grand daughter, so here is the question. What does it mean when the pattern says "Work even St st until armholes measure 8 ins or 20.5 cm. Is that measurement around the arm holed?

It means to keep knitting in stockinette stitch (knit one row, purl one row) just as you have been doing without any increases or decreases until you have 8 ins from the beginning of the armhole shaping or the armhole marker. It’s usually a little less than half of the actual armhole that you would measure around the armhole.

You would measure straight up from the first row you began the armhole shaping on, which would either be BO x sts or decreases.