The short answer is: We don't know! It's YOUR finger!
We highly, really, truly suggest (beg) you go to a professional jeweler's for in-person measuring if you aren't 100% positive about your ring size. And we suggest you do this at least twice and during different parts of the day. Fingers swell and, well, un-swell, at different times throughout the day. Figure out what works best for you and then use that measurement to order your correct ring size.
There are printable sizers online, suggestions for how to measure using a piece of string, etc...these are NOT good methods and probably won't be accurate.
We don't have ring sizers for sale. Some larger websites do have them available for around $12 to $20, but we just don't carry them right now. The fewer things we have to stock, the lower our prices will be for our amazing wedding bands. We're sure you understand.