Borrow a ring your partner currently wears on their ring finger (or middle finger, which is usually a half-size larger) and trace the inside circumference on a piece of paper. A jeweler can use this circle to determine the diameter.
Fingers tend to swell throughout the day. It is best to measure in the evening when the hands are warmest. how do you know what size engagement ring to buy
If you are still uncertain, prioritize a ring design that is easy to alter. with a plain metal band are the easiest to resize. Conversely, eternity bands (where diamonds go all the way around) and certain tension settings are often impossible to resize without completely rebuilding the ring. Borrow a ring your partner currently wears on