If you’re looking to get a ring,
but can’t for whatever reason provide the finger the ring is intended for, I found an online ring sizer that doesn’t require you to print out a page and fiddle with strips of paper.
https://www.jewelrywise.com/tools-resources/ring-sizer
Basically? They put an image of a standard-issue credit card on screen. You hold a card of that size (credit, library, whatever, who cares) up and size the image to match the real thing, because monitor resolutions and zoom factors are fiddly beasts. Once you’ve got them matching, you click Next and they put a circle on screen, using the information from the prior stage to ensure that it’s an accurately sized match for U.S. ring size 7. You can now hold a ring that fits the finger you’re buying for up to that circle and adjust the circle size up or down until it matches the inner circumference of the real ring; it’ll tell you what ring size the circle corresponds to, and hooray, you can now get a ring that fits.
Makes it easier for me to tell people what size rings I’ve made, I’ll tell you that.