This might have been posted previously, but I found it when preparing for a new project - an arm bracer. This seems to be the simplest, cheapest way to get an exact sizing for the leather necessary for a bracer: http://kamuicosplay.deviantart.com/art/Armor-Pattern-Tutorial-416269738
I'm guessing that you could use this to correctly size about anything, hats, wrist bands, corset, etc.
T.