Your ring should fit your finger comfortably—snug enough so that it will not fall off, but loose enough to slide over your knuckle with some resistance.
Here's how to measure your ring size at home:
Cut a thin strip of paper or use a piece of string.
Wrap the paper or string around the base of the finger you want to measure. Make sure it fits comfortably and isn't too tight or too loose.
Mark the spot where the paper or string overlaps, forming a complete circle.
Measure the length of the paper or string from the starting point to the mark in millimeters.
Use the following chart to determine your ring size based on the measurement:
This method should give you an accurate measurement of your ring size.