Ring size is a measurement of the inside of the ring - either its diameter or, more usefully at home, the circumference of the finger it has to fit. US sizes run in half-size steps, and each half size is only about 1.3 mm of circumference, which is why small measuring errors change the answer. The good news is that there are three dependable home methods, and using two of them cross-checks the result.
Whichever method you choose, measure at the end of the day, when fingers are at their largest, and at a comfortable room temperature - cold fingers measure smaller. Measure the exact finger the ring will be worn on: most people's left and right hands differ by half a size or more, and the ring finger and middle finger of the same hand differ too. For the jewelry side of sizing, the Apparel Search rings guide covers styles and settings once the size is known.
Method 1: Measure a Ring That Already Fits
If a ring already fits the right finger, measure it instead of the finger - it is the most accurate home method. Lay the ring on a ruler or caliper and measure the inside diameter: the distance across the center of the ring, inside edge to inside edge, in millimetres. Then read the size from the chart below. A ring with an inside diameter of 17.3 mm, for example, is a US size 7.
Take the measurement twice, across two different axes, and average them; a worn ring can be very slightly out of round. If you have calipers, they are easier to read to a tenth of a millimetre than a ruler, and a tenth matters - half a size is only about 0.4 mm of diameter.
Method 2: The Paper Strip or String Method
Cut a thin strip of paper about 10 cm long, or use a length of non-stretch string or dental floss. Wrap it around the base of the finger, snug but not tight - the fit of a ring that slides on with slight resistance over the knuckle. Mark where the end meets the strip, lay it flat, and measure the length in millimetres. That length is your finger's circumference; find it in the chart below and read across to the US size.
The strip must pass over the knuckle, so wrap and slide it off the way a ring would move. If your knuckle is much wider than the base of your finger, measure both places and choose a size between the two - large enough to pass the knuckle, small enough not to spin at the base. Paper stretches less than string and is easier to mark; avoid elastic materials entirely.
US Ring Size Chart
Standard US ring sizes with their inside diameters and circumferences. EU sizes are simply the circumference in millimetres, rounded - a useful cross-check when shopping European jewelers.
| US size | Inside diameter (mm) | Circumference (mm) |
|---|---|---|
| 5 | 15.7 | 49.3 |
| 5.5 | 16.1 | 50.6 |
| 6 | 16.5 | 51.9 |
| 6.5 | 16.9 | 53.1 |
| 7 | 17.3 | 54.4 |
| 7.5 | 17.7 | 55.7 |
| 8 | 18.1 | 57.0 |
| 8.5 | 18.5 | 58.3 |
| 9 | 18.9 | 59.5 |
| 9.5 | 19.4 | 60.8 |
| 10 | 19.8 | 62.1 |
| 10.5 | 20.2 | 63.4 |
| 11 | 20.6 | 64.6 |
| 11.5 | 21.0 | 65.9 |
| 12 | 21.4 | 67.2 |
Method 3, for confirmation: an inexpensive plastic ring sizer - a set of graduated rings or an adjustable loop - removes the marking and reading errors of the strip method. Jewelers also size free in store, which is worth doing before an expensive or hard-to-resize purchase such as an eternity band.
Fit Tips Before You Order
- Between two sizes, choose the larger - especially for wide bands, which feel tighter than thin bands at the same size. For bands wider than about 6 mm, many jewelers suggest going up half a size.
- Consider the knuckle. The ring must pass the knuckle but sit steadily at the base; if the two measurements disagree, split the difference.
- Mind the season. Fingers swell in heat and shrink in cold. A size measured in winter may feel snug in August; measuring in mild conditions, later in the day, gives the safest average.
- For a gift, borrow a ring the person wears on the same finger and measure its diameter, or trace its inside circle on paper. Guessing from a photo or another finger is the least reliable route.
Common Questions
- What if I am between ring sizes?
- Choose the larger size. A ring that is slightly loose can be adjusted with sizing aids and is easy for a jeweler to take down, while a ring that is too small may not pass the knuckle at all. This matters even more for wide bands, which fit tighter at the same labeled size.
- Does ring size differ between the left and right hand?
- Usually, yes. The dominant hand is often half a size larger, and corresponding fingers on the two hands are rarely identical. Always measure the specific finger the ring will be worn on.
- How do I measure ring size for a surprise gift?
- Borrow a ring the recipient already wears on the same finger and measure its inside diameter against the chart. If borrowing is impossible, a paper-strip measurement of a similar finger is a fallback, and choosing a resizable style or the larger of two candidate sizes limits the risk.
- Can every ring be resized later?
- No. Plain bands usually resize well, but eternity bands with stones all the way around, tension settings, and some patterned or alternative-metal rings cannot be resized or can only be adjusted within narrow limits. For those styles, confirm the size with a jeweler's sizer before ordering.
Measure & Convert: The Full Series
This page is part of the Apparel Search measuring and size conversion series. Browse the full series below, or start from the size guides hub.