Method 1: You already have a ring that fits

If you have a ring that already fits well, it’s easiest to use that one. Take a ruler and measure the diameter of the inside of the ring (not the rim). The number of millimeters is your ring size, so if you measure 17 mm, your size is 17.

Method 2: You don't have a ring that fits

Next, measure the circumference of your finger with a piece of string. Wrap a piece of string around your finger—be careful not to pull it too tight; it still needs to go over the knuckle! Take a ruler and lay the string on top of it.

Also good to know

1. Each of your 10 fingers is different, so the ring sizes for your fingers may vary. That's why you should always measure the finger on which you plan to wear the ring!
2. Keep in mind the thickness of the ring; the thicker the ring, the tighter it will fit. For a very thick ring, choose a half size (0.5 mm) larger, and for a very thin ring, choose a half size (0.5 mm) smaller.
3. If you're unsure between two sizes, in our experience, the larger size often fits better.
4. Don't try to measure your finger if your hands are cold or very warm, because heat causes your fingers to expand. After exercising, after a walk, or right after waking up are also not good times to measure. Measure your finger when your hands are at a normal temperature.
5. Do you want to be as sure as possible? Then take measurements at two different times on two different days.