I am looking to created a template for helmet decals like the above image and want to have it sized correctly before it goes to print. Can anyone point me in the right direction on how to go about measuring? Thanks!
To fit art to this helmet you need to know the size and shape of the helmets surface when it is laid flat.
I can tell you 2 ways to obtain the flat dimensions:
contact the manufacturer or the company that decals them and ask for a decal template. (alternatively find a decal manufacturer that makes decals for many helmets and use a similar one or find the exact one on their site and copy it. This look like yours: http://schoolpride.com/Helmet-Decals/Lacrosse-Helmet-Decal-Package)
Remove the helmet shell (if available) and lay it flat, cutting as little as possible. Measure the flattened shell, or scan it with a flatbed. Use the new shape dimensions as outlines for your art.