Votive Placecards Question

I plan on making votive placecards, and have a question about cutting out the vellum paper. I found these instructions

Step One: Measure your votive holders to determine the approximate height and length around. Using these measurements, make a template of the shape of your label. Note that even the most plain votive holders will have a slight curvature, so expect the template to be in an arch shape...

So how do I know how much of an arch the template needs? Does anyone know if there is a template I can download and print somewhere? Or will it work fine if I just cut it straight, like with a paper cutter?
Thanks!