This is a ring maker I made for myself using OpenScad to visualise wedding bands I was considering. It lets you configure any ring size to the three patterns: Beveled, Rounded, and Faceted. Each ring also has a rounded inner comfort finish. 

The print profile has all three designs in US 10.5 at 8mm wide.

Basic PLA printed true to size for me.

You can also change the rings thickness and each designs parameters. More or less the defaults do a good job.
You can set the ring width, size (US or International), and the ring thickness.

The facets are generated randomly and you can adjust them easily.

You can use this model to figure out your ring size. I checked for any print variations or shrinking via a pair of calipers. The US/Canada sizes are based on this chart. 

I recommend printing a half size or .5mm larger than what you measure because the layer lines increase friction. Finer layer lines will also result in a better ring, as goes for a smaller nozzle.

Please post images of your results and feedback on the model. 

Boosts, likes, and ratings are also appreciated!