How should it fit?
How To Measure Your Ring Size
The ring should fit your finger comfortably: snug enough so it won't fall off, but loose enough to slide over your knuckle with relative ease. A little wiggle over the knuckle is good. When the knuckle is bigger than the base of the finger, measure both places and pick a size in between the two.
Size Difference
The difference from one whole ring size to the next is a matter of 2-3mm in the circumference of the inner part of the band.
Variances
Many people find that a variance of a half size or less will still fit comfortably most of the time.
The wider the ring, the tighter it will fit on a finger. For anything 5mm+ in width, go a half size up.
The interior of a Comfort Fit ring puts less metal in contact with the finger, so they tend to fit a little loose. If you’re between sizes, round down. If you have large knuckles, you may need to go up a half size.
It’s also good to keep in mind that finger size fluctuates slightly based on diet, temperature and activity. The way your ring fits may change slightly over the course of a single day.