u/Dunkan_404

I'm planning to make a V1 Ultrkill mask out of cardboard. So far, I've done a quick sketch on paper, but I realized I don't know how to properly measure my head to create the helmet. Do I even need to measure my head, or is this a case of trial and error?

And maybe someone has advice on how to properly draw the helmet in three projections (front, side, top)?