Why ring sizes are not universal
Ring sizing systems differ by country, and even within the US system a size is a range rather than a fixed point. A US size 7 covers an inside circumference of about 54.4mm, and a ring that measures 54.2mm or 54.6mm will still be sold and worn as a 7.
That tolerance is why a ring bought online at your usual size can feel different from the one already on your hand. Band width, band profile, and the shape of your knuckle all change how a given size fits.
Two methods below will get you close. Neither replaces a fitting at a jeweler if one is available, but both are accurate enough to order from, especially with the size-up rule at the end.
Method one: measure a ring that fits
Take a ring that fits the intended finger well, on the hand it will be worn on. Rings fit differently on the dominant hand, which is usually slightly larger.
Place it on a flat surface and measure the inside diameter across the widest point, from the inner edge of one side to the inner edge of the other. Measure in millimeters, and measure three times, taking the middle reading.
Do not measure the outside of the band. A wide band adds two to four millimeters of metal to the outside diameter, which would put you one to two sizes too large.
A ruler with millimeter marks is enough for this. Calipers are better if you have them, since a half millimeter changes the size.
Method two: the paper strip
Cut a strip of paper about 10mm wide and 100mm long. Wrap it around the base of the finger, below the knuckle, snug but not tight. Mark the point where the paper overlaps itself.
Lay the strip flat and measure from the end to the mark in millimeters. That number is the inside circumference, which converts directly to a size on the chart below.
A few details decide whether this works. The strip should slide over the knuckle with slight resistance, not drop off. If it slides on easily, the size is too large. If it will not pass the knuckle at all, it is too small regardless of what it measures at the base.
| US size | Inside diameter | Inside circumference |
|---|---|---|
| 4 | 14.9mm | 46.8mm |
| 5 | 15.7mm | 49.3mm |
| 6 | 16.5mm | 51.9mm |
| 7 | 17.3mm | 54.4mm |
| 8 | 18.1mm | 57.0mm |
| 9 | 18.9mm | 59.5mm |
| 10 | 19.8mm | 62.1mm |
| 11 | 20.6mm | 64.6mm |
| 12 | 21.4mm | 67.2mm |
Band width changes the fit
A wide band feels tighter than a narrow one at the same size. The skin under the band is compressed across a larger area, and there is less room for the finger to spread.
The usual adjustment is a quarter to a half size up for bands of 4mm or wider, and a full size up for bands of 8mm or more. A 2mm band at size 7 and an 8mm band at size 7 are not comfortable in the same way.
Stacking rings compounds this. Three 2mm bands worn together behave like a 6mm band, so the stack usually needs to be a half size larger than the individual rings.
Timing and temperature
Fingers swell through the day and in heat. A finger measured first thing in the morning can be half a size smaller than the same finger measured in the late afternoon.
Measure at the end of the day, at room temperature, and not right after exercise, a hot shower, or a long walk in summer heat. Cold hands read small, which produces a ring that fits in winter and binds in July.
If two readings disagree by more than half a size, take the larger one. A ring that spins is annoying. A ring that will not come off over a knuckle is a problem.
Knuckles and other exceptions
A knuckle wider than the base of the finger is common and it limits how small a ring can be. Size for the knuckle, then accept a slightly loose fit at the base, or choose a design that can be adjusted later.
Wide knuckles also argue for a lighter setting. A tall stone on a loose ring tips sideways, and a low bezel stays put.
Before you order
- Measure the correct finger on the correct hand, at the end of the day.
- Confirm the reading with the second method if you can.
- Add a half size for bands over 4mm wide, and a full size over 8mm.
- Write the millimeter measurement in the order notes, not only the size number.
- Ask about resizing terms before the ring is cast.
Every ring we make is built to the size on the order, and gold and platinum rings include one free resizing within 12 months, up to two sizes. The full terms are on the ring size guide, and sizing questions can go to contact before the CAD render is approved, which is the cheapest point to change anything.