Select a ring which fits the finger you plan on wearing your new ring and a ruler.
Choose preferably a ring void of stones and ornaments to facilitate the measurement
Rest the ring on the ruler to measure the ring’s diameter
Report the measurement on the conversion table
Select a ribbon (tissue or paper) , a ruler and a pencil. Ideally, take the measurements in a room temperature environment to prevent your fingers from changing size due to the heat/cold.
Start by marking a reference point on the ribbon with your pencil
Wrap the ribbon around the finger on which the ring will be
Trace a second marking above the first reference point
Unwrap the ribbon and measure the distance between both reference points