Choose your pairing together

A surprise gift can be heart-fluttering. However, when it comes to matching rings, surprise gifts are not recommended. Does the person you want to give the gift to normally wear rings? If they like rings, you'll be able to figure out their size and preferences. However, if they don't normally wear rings, it's possible they have a metal allergy or avoid rings for work reasons.
If you have a metal allergy, you can get a patch test at a hospital to find out the causative substance, so you can avoid it. Another effective method is to choose materials such as platinum and gold, which are known to be less likely to cause allergies.

Many people who work in strict hygiene-related workplaces, such as food and beauty-related industries, tend to avoid wearing rings. In such cases, why not try using it as a pendant head? You can wear it as a ring on your days off and as a pendant on your days off.
Also, if you want to wear it every day, the size will depend on which finger you choose to wear it on. Even if you're giving it to someone because "I heard it was size X," some people may want to wear matching rings on a different finger. It can be fun to discuss whether you want it on the hand you always hold together, or on opposite hands. Make the time you spend choosing it a treasure.