If you have access to a ring that your partner already wears on their left ring finger, you can measure it using a ring sizer. This method is one of the most reliable, as it uses a ring that your partner already wears there.

If you can't use an existing ring, try taking a discreet measurement of your partner's finger with a tape measure or piece of string. This will give you an approximate size, which you can confirm later with a jeweler.

Many jewelers, like LeDiamanti, offer a free resizing service after the proposal. This means you can choose a standard size at the time of purchase and adjust it later if necessary. This flexibility is especially useful if you are unsure of the exact size.