A superhero cape is a super-easy pattern to make, since it's simply a trapezoid. My pattern piece is a half trapezoid, meant to be placed on the fold and cut:
The length of the pattern piece is the total finished height of the superhero cape, plus an inch at the top to fold over the elastic neck piece. The top width is half of the total finished top width, and the bottom width is half of the total finished bottom width.
Now that I know one or two specific sizes that I prefer for these capes, having a pattern piece is MUCH easier than measuring out each individual cape.