If you already know your size for the finger that you want to wear the ring on, you can use that size.
If you are buying a ring for her
The best way to find her ring size is to ask her friends or family who usually know this type of information.
Otherwise, follow these simple steps below to find your size
What you need: a pen, a ruler, and a piece of non-stretchy string. For the string, please don't use paper because it is less accurate. Floss works! :)
Step 1: Determine the finger that you want to wear the ring on. Wrap the string snugly around the base of that finger.
Step 2: Mark where the string overlaps. You should see two marks on your string.
Step 3: Measure the distance between the two marks. This distance is the inside circumference of your ring.
Step 4: Find your ring size by matching your measurement to the closest insider circumference (3rd or 4th column) in the chart below. Keep in mind that your fingers may swell sometimes, so you might want to leave a little more room.