Education
Measuring a Ring Size at Home, Accurately
Measure an existing ring rather than a finger, send millimetres rather than a size, and do it at the right time of day.
Written by the Mapple Gems workshop, Surat Β· Updated 9 September 2026
Short answer
The most accurate home method is to measure the inner diameter of a ring that already fits, using a ruler with millimetre markings, and send that number. Do not convert it to a size β five incompatible sizing systems are in use worldwide and double conversion is the commonest cause of a ring that does not fit. Measure at the end of the day at room temperature, and check knuckle clearance separately from the base of the finger.
Ring sizing goes wrong more often than any other part of ordering jewellery, and almost always for one of three reasons: the wrong time of day, a conversion error, or a knuckle that was never accounted for. All three are avoidable in about five minutes.
Method one: measure a ring that fits (best)
- Choose a ring worn on the same finger of the same hand. Not a different finger β the sizes differ substantially.
- Lay it flat on a ruler with clear millimetre markings.
- Measure across the inside, from one inner edge to the opposite inner edge, through the centre. That is the inner diameter.
- Measure twice, at right angles β if the two differ, the ring has gone slightly out of round, and the larger figure is closer to correct.
- Send the number in millimetres, to one decimal place, and say which finger and hand it came from.
Typical inner diameters run from about 14Β mm to 21Β mm. A tenth of a millimetre is roughly a quarter size, so reasonable care with a ruler is enough.
Method two: a paper strip (adequate)
If there is no ring to measure, wrap a strip of paper or a thin strip of thread around the base of the finger, mark where it overlaps, lay it flat and measure the length. That is the circumference, which is equally unambiguous β just say which measurement you are sending.
Two cautions. Paper does not stretch and thread does, so paper is more reliable. And it must be snug but not tight β pulled tight, it produces a ring that will not go on.
Send millimetres, never a converted size β this is where most sizing errors are created. Five incompatible systems are in use: US numbers, UK and Commonwealth letters, European millimetre circumference, a French convention that differs from the European one by 40, and Japanβs own 1β27 scale. Each conversion introduces rounding, and double conversion β you converting to a size, then the workshop converting back β compounds it. We have seen rings arrive a full size out for exactly this reason, with nobody at fault. Inner diameter or circumference in millimetres means the same thing in every country and in every system. Measure once, send that number, and the problem disappears.
When to measure
| Condition | Effect | Do this |
|---|---|---|
| Cold morning | Fingers at their smallest | Avoid β ring will be too tight later |
| End of day, room temperature | Closest to typical | Measure now |
| Just after exercise | Noticeably swollen | Wait an hour |
| Hot weather | Larger than average | Measure indoors |
| Dominant hand | Usually a quarter to half size larger | Say which hand |
The knuckle question
The second most common problem, and it needs two measurements rather than one.
A ring has to pass the knuckle and then sit at the base of the finger. For most people those are close enough that one size works. For anyone with slim fingers and proportionally larger knuckles β common, and more so with age β they are meaningfully different, and sizing to the knuckle leaves the ring loose and spinning below.
Measure both, and say so. The answer is not a compromise size: it is a ring sized to the knuckle with sizing beads inside the shank to hold it at the base, or a euro shank with a flattened underside that resists rotation by design.
Things that change the size you need
- Band width. A wide band fits more snugly than a narrow one at the same nominal size β above about 6Β mm, expect to go up a quarter to half size.
- Comfort fit. A domed interior contacts less of the finger, so comfort-fit rings often need a half size smaller than the same size with a flat interior. State which you are ordering.
- Profile height. A tall setting rolls more when a ring is even slightly loose, so a high ring wants a snugger fit than a low one.
- Stacking. Two rings worn together sit slightly differently from one alone.
If it is a surprise
Measuring a ring they already own is the reliable route β borrow one worn on the correct finger, measure it, and put it back. A ring from a different finger is a guess, and the difference between an index and a ring finger can be a full size or more.
If nothing is available, order slightly large rather than slightly small. A loose ring can be worn carefully until resized; a tight one cannot be worn at all, and it turns a happy moment into an immediate errand.
Before you order
Ask two things: how many sizes this design can be resized, and who pays for the return leg if it needs adjusting. Full eternity bands cannot be resized at all, channel-set and fully pavΓ© shanks are limited, and on an international order a resize means a second customs clearance as well as a second round trip.
Keep reading
- Importing jewellery: what changes by country
- Shank styles explained β including the euro shank
- Wearing rings on other fingers
Frequently asked questions
What is the most accurate way to measure a ring size at home?
Measure the inner diameter of a ring that already fits the correct finger, using a ruler with millimetre markings, from one inner edge through the centre to the other. Measure twice at right angles β if they differ the ring has gone out of round, and the larger figure is closer to correct. Send that number in millimetres.
Why should I give millimetres instead of a ring size?
Because five incompatible sizing systems are in use worldwide, and each conversion introduces rounding. Double conversion β you converting to a size and the workshop converting back β compounds it, and can put a ring a full size out with nobody at fault. Inner diameter or circumference in millimetres means the same thing everywhere.
What if my knuckle is bigger than the base of my finger?
Measure both and say so. The answer is not a compromise size but a ring sized to pass the knuckle with sizing beads inside the shank to hold it at the base, or a euro shank β flattened along the underside β which resists rotation by design.
Does band width change the size I need?
Yes. A wide band fits more snugly at the same nominal size, so above about 6Β mm expect to go up a quarter to half size. Comfort fit works the other way β a domed interior contacts less of the finger, so those often need a half size smaller than the same size with a flat interior.
Send us the millimetres.
Inner diameter, which finger, which hand. We will do no conversions at all β that is the point.
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