Finding the Right Ring Size at Home

Why a snug fit matters with onyx and gemstone rings

Onyx is a striking stone — deep, glossy and often cut as a generous cabochon — and a well-made onyx ring is a pleasure to wear daily. But it is also a stone that tends to be set in a substantial mount, sometimes a full bezel, sometimes a wide flat shank. Those settings do not forgive a poor fit. A ring that spins will drag the stone against your neighbouring fingers, and a ring that pinches will make you take it off within an hour.

There is another reason to get it right first time. Rings set with gemstones can often be resized, but it is more involved than adjusting a plain band — heat and pressure near a stone always carry some risk, and some settings simply will not allow it. Measuring your finger properly at home takes ten minutes and saves a great deal of disappointment.

Before you begin: a few simple tools

You do not need anything specialist. Gather the following:

• A strip of plain paper or thin card, about 10cm long and 1cm wide
• A pen or fine-tipped pencil
• A ruler marked in millimetres
• A ring you already own that fits the same finger well
• A few minutes in a warm room

Avoid string and fabric tape measures entirely. Both stretch as you pull them, and a millimetre of stretch is the difference between two whole sizes.

Method one: the paper strip

Wrap the paper strip around the base of the finger you are buying for, just below the knuckle. Pull it snug — tight enough that it will not slip down, but loose enough that it would slide over the joint without force. Mark the paper with a single clear line exactly where the leading edge meets the strip.

Lay the strip flat beside your ruler and measure from the end to your mark in millimetres. That figure is your finger's circumference. Repeat the whole process twice more and compare: if your three readings differ by more than a millimetre, measure again rather than averaging.

To convert, divide your circumference by 3.142 to get the internal diameter. Most jewellers list both figures, but if only a UK letter size is shown, useful landmarks are 51mm (roughly an L), 54mm (around an N) and 58mm (close to a Q). Sizes between L and Q cover most women's ring fingers; S to X, roughly 60mm to 67mm, covers most men's.

Method two: measuring a ring you already own

This is often the more reliable method, because the ring already has to clear your knuckle. Choose a ring that fits the correct finger comfortably, then measure its internal diameter — never the outside edge, which includes the metal thickness and will leave you with a ring that is far too big.

Place the ring flat on your ruler and measure from the inner edge on one side to the inner edge on the other, reading to the nearest half millimetre. Alternatively, trace around the inside of the band onto paper with a fine pen and measure across the circle. Because onyx rings are often wide, a ring with a broad band will need to be a little larger than a narrow one for the same finger, so treat this measurement as a starting point if the band widths differ.

Small details that change your measurement

Fingers are not fixed objects. They change size through the day and with the weather, and a few of these shifts are surprisingly large:

• Time of day. Fingers are at their smallest first thing in the morning and their largest in the late afternoon and evening. Measure in the afternoon or early evening.
• Temperature. Cold hands can shrink by half a size or more. Measure indoors, with warm hands, never after coming in from a winter walk.
• Your knuckle. If your knuckle is wider than the base of your finger, choose a size that clears the knuckle comfortably — the ring may feel slightly loose at the base, which is normal and correct.
• Band width. For bands of 6mm or more, go up half a size or to the next letter. The same applies if you plan to stack the ring.
• Your dominant hand. It is usually a fraction larger, so measure the actual hand you will wear the ring on.

Falling between two sizes

You will often land between two letters, and this is where a little judgement helps. For a chunky onyx ring worn every day, err on the larger side. A ring that is marginally loose sits flat, slides over the knuckle without a struggle and can be adjusted later with sizing beads or a small insert. A ring that is marginally tight will be uncomfortable within minutes and is far harder to live with.

The exception is a very narrow band of 3mm or less with a small, light stone, where a snugger fit is less likely to twist. When in doubt, note both sizes and mention them when you order — most jewellers will happily advise which suits the specific design. A few careful measurements now mean your onyx ring arrives ready to wear and stays that way.