To determine the correct ring size for your partner, you can either secretly borrow one of their existing rings and have it measured at a jeweler's store or use a printable ring size chart available online. Alternatively, you can consult with a jeweler who can guide you in finding the right size based on your partner's finger measurements.
It's important to note that these answers are general and may vary based on individual preferences, jeweler recommendations, and evolving trends in Belgium.