/ic/ - Artwork/Critique

How can I get the proportions right when starting from a gesture? I always get the head too big like in pic related. My aim isn't to match the reference 1:1 but I want to at least get the proportions right.

Like in pic related, the head is way too wide. I tried to make the images the same size as possible but they're not exactly the same size. But in the photo the side of her head to the end of the shoulder is about 1 head width, in my drawing it's only 3/5th. But if I widen the arm then the arm just looks way too fat.