Measuring an armhole is a tricky thing to get accurate because of the curved line. You have to start with the stitching line since the outer edge of different pattern curves can be different lengths for the same stitching line. Also, the stitching line to be measured needs to eliminate the beginning and ending seam allowances, so that comparisons to the sleeve head are easier. Once you understand the armhole measurement, measure the sleeve head to see what ease is drafted in. If you have a woven pattern and want the fabric to be a knit, you will want less ease (approx. 1/2 inch for a knit sleeve head) or if you want a jacket made in leather you will definitely not want a lot of ease in the sleeve head. I personally don’t like a front armhole of a knit top with less than 8 inches in length because it feels too tight to me.
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