Rings are the only jewellery with a genuine sizing problem, and the simplest solution is to buy something else. Necklaces have a length rather than a size, and a fine chain between sixteen and eighteen inches suits almost everybody. Earrings have no size at all. Bracelets have some tolerance, and an adjustable chain bracelet or a slightly generous one is comfortable across a wide range of wrists. Anklets are similarly forgiving. Between those you have most of the good gifts in jewellery available with no measurement required. If you are set on a ring, there are two honest routes. Buy an adjustable or open band, which reads as a design choice rather than a compromise. Or buy the ring you want and accept that resizing is part of the gift, which is a perfectly normal thing to say out loud when you hand it over. What does not work is guessing and hoping, because a ring that does not fit is a ring nobody wears.

The reliable method is to borrow a ring she already wears and take it to a jeweller, who will measure it in thirty seconds for nothing. Take one from the correct hand and the correct finger, because those differ by up to a full size on most people, and fingers on the dominant hand tend to be larger. If borrowing is impossible, the printable sizing charts are less accurate than they claim, largely because printers scale, and the paper strip methods overestimate. A better fallback is to note that the most common women's sizes cluster in a narrow band, and to buy in the middle of it while keeping the receipt and confirming the returns window covers resizing. Two further points. Knuckle size, not finger size, decides whether a ring goes on, so anybody with larger knuckles needs a size that will then spin. And a wide band fits more tightly than a narrow one at the same nominal size, so a chunky ring wants a half size up.

Buy the necklace. This is the one situation where we would abandon the idea of the ring entirely, because the failure mode is so specific and so disappointing. A fine chain with a single bezel-set stone is close to universally wearable, needs no measurement, and is the gift people report wearing years later. If it must be a ring, buy an open or adjustable one and say nothing about sizing at all. And if you are buying an engagement ring, borrow a ring, because that is a purchase where guessing is not acceptable and where every jeweller expects to be asked. What we would not do is buy a ring one size too large on the theory that it can be taken in, since resizing down a set band is more disruptive than resizing up. If you take one thing away, take a ring she already wears to a jeweller, because it is free and it takes a minute.