Step 1: Choose an existing ring that fits the finger of choice.
Step 2: Measure the inside diameter of the ring (see image for reference).
Step 3: Reference the chart to find your ring size.
Option 2: Measure your finger
Fingers are likely to swell after drinking alcohol or exercising, and likely to shrink in cold weather. Fingers should be measured when they are in their normal state.
Step 1: Wrap a piece of string/thread (string should not be elastic or stretchable) or strip of paper tightly around the finger you plan to wear the ring on. Make it tight, as this will provide the most accurate measurement.
Step 2: Draw a mark or cut closely along the point where the two ends meet.
Step 3: Use a ruler to measure the length. Reference the chart to find your ring size.