You need two things: a millimetre ruler and five quiet minutes. Everything else in this guide exists because the same handful of small mistakes — measuring cold hands, using stretchy string, forgetting the knuckle — is what puts people a size out.
There are two honest ways to do this at home. If you already own a ring that fits the finger, measure the ring: it is the more accurate of the two. If you do not, measure the finger with a strip of paper. Both end in the same place: a number in millimetres that converts to a US size.
Method 1: measure a ring you already wear
- 1. Choose the right ringIt has to be a ring that fits the finger you are sizing for — not a ring that fits a different finger, and not one you have not worn for years.
- 2. Lay it flat on the rulerRead the inside diameter: inner edge to inner edge, straight across the widest point. Not the outside of the band.
- 3. Read to the nearest half millimetreHalf a millimetre is roughly a half size, so this is worth doing carefully, in good light.
- 4. Do it three timesMeasure, look away, measure again. Take the middle reading rather than the first one.
Method 2: measure the finger with paper
- 1. Cut a strip of paperAbout 5 mm wide and long enough to wrap around the finger. Ordinary printer paper. Not string, not thread, not elastic.
- 2. Wrap it at the base of the fingerSnug, flat against the skin, not tight enough to dent it. Snug is the word to hold on to — a ring should slide, not squeeze.
- 3. Mark the overlap and lay it flatMark exactly where the end meets the strip, unwrap it, and measure to the mark in millimetres. That figure is the inside circumference.
- 4. Test the knuckle before you trust itTape the strip into a loop at the size you measured and slide it over the knuckle. If it will not pass without forcing, you need the knuckle measurement instead.
Millimetres to US ring size
Find your measurement in the column you used. The two columns describe the same ring — diameter is straight across, circumference is all the way round.
| US size | Inside diameter | Inside circumference |
|---|---|---|
| 4 | 14.9 mm | 46.8 mm |
| 4½ | 15.3 mm | 48.0 mm |
| 5 | 15.7 mm | 49.3 mm |
| 5½ | 16.1 mm | 50.6 mm |
| 6 | 16.5 mm | 51.9 mm |
| 6½ | 16.9 mm | 53.1 mm |
| 7 | 17.3 mm | 54.4 mm |
| 7½ | 17.7 mm | 55.7 mm |
| 8 | 18.1 mm | 57.0 mm |
| 8½ | 18.5 mm | 58.3 mm |
| 9 | 18.9 mm | 59.5 mm |
| 9½ | 19.4 mm | 60.8 mm |
| 10 | 19.8 mm | 62.1 mm |
| 10½ | 20.2 mm | 63.4 mm |
| 11 | 20.6 mm | 64.6 mm |
| 11½ | 21.0 mm | 65.9 mm |
| 12 | 21.4 mm | 67.2 mm |
Between two rows? Take the larger size. A ring that is a little loose can be brought down cleanly; a ring that will not pass the knuckle cannot be worn at all.
Five things that put people a size out
1. Measuring at the wrong time of day
Fingers are smallest in a cold morning and largest in a warm evening or after salt, exercise or a long flight. The swing is close to half a size, which is exactly the difference between comfortable and stuck. Measure late in the day, at normal room temperature.
2. Using string
String stretches, and it stretches differently every time you pull it. Paper cannot. If all you have is string, do not trust the result to half a millimetre — and do not use elastic or a rubber band at all.
3. Forgetting the knuckle
The ring has to pass the knuckle and then sit at the base of the finger without spinning. If your knuckle is much wider, size for the knuckle and accept that the ring will turn a little — or ask about sizing beads, which are small additions inside the band that hold it upright. That is a decision to make with your jeweler, not on a chart.
4. Ignoring the width of the band
A wide band sits tighter than a thin one at the same measurement, because it covers more of the finger. For a band around 6 mm or wider, go up a half size from what you measured.
5. Measuring the wrong hand
Your dominant hand is usually a touch larger. Measure the hand and the finger the ring will actually live on.
One thing not to do: do not try to open or close a ring yourself with pliers, and do not have a band “stretched” at a counter. Forcing metal thins the shank, can crack a solder join and loosens stones in the setting — and undoing that costs more than resizing it properly in the first place.
If you would rather not guess
You do not need to know your size to send a ring in. Tell us it is loose or tight and our jewelers measure the ring itself when it reaches the bench — which is more accurate than any measurement taken at home. Your written quote confirms the finished size before any work begins, and nothing is worked on until you approve it.
Ring sizing, prong re-tipping and shank work all sit in the same group, starting at $49. The kit, the shipping in both directions and the inspection are free, and if you decline the quote the ring ships back to you free and fully insured.
Where to go next
Frequently asked questions
How do I measure my ring size at home?
The most reliable home method is to measure a ring that already fits that finger: lay it on a millimetre ruler and read the inside diameter from inner edge to inner edge. A US size 6 is about 16.5 mm across, a size 7 about 17.3 mm, and a size 8 about 18.1 mm. If you have no ring to measure, wrap a narrow strip of paper around the base of the finger, mark the overlap and measure that length as the inside circumference.
Should I use string to measure my ring size?
String works only if it does not stretch, and most string does. A strip of ordinary paper about 5 mm wide is more accurate because it cannot stretch and it lies flat against the finger. Never use elastic, thread or a rubber band.
What time of day should I measure my finger?
Late in the day, at normal room temperature, and when your hands are neither cold nor swollen. A finger can change by close to half a size between a cold morning and a warm evening — and that is exactly the margin between a ring that fits and one that does not.
What if I am between two ring sizes?
Go up, not down. A ring that is slightly loose can be sized down cleanly, while a ring that will not pass the knuckle cannot be worn at all. Add another half size if the band is wide, roughly 6 mm or more, because a wide band sits tighter than a thin one at the same measurement.
Do I need to know my size before I send a ring in for resizing?
No. You can tell us the size you want, or simply tell us the ring is too loose or too tight and send it in. Our jewelers measure the ring itself when it reaches the bench, and your written quote confirms the finished size before any work begins.
Can every ring be resized to the size I measure?
Most rings, yes. Some full-eternity and tension-set designs cannot be sized conventionally. If your ring is one of them we say so honestly and suggest the best alternative rather than forcing the work.