Quick answer: Measure the inner diameter of a ring that already fits, in millimeters, then match it against a standard size chart — or calibrate your screen to a physical ruler and drag a digital circle until it matches the ring's inner edge. Accuracy improves when you measure in the evening, at room temperature, and cross-check with two methods before ordering.
Grab any physical ruler. Hold it flat against your screen and drag the slider until the bar below lines up exactly with the 50mm mark.
Lay a ring that fits you over the circle below, then use the slider or +/- buttons so the circle matches its inner edge.
Use a non-stretchy strip of paper or string, wrap it snugly around the base of your finger, mark where it overlaps, then lay it flat against a ruler.
Search or sort by any column to cross-reference inner diameter and circumference against US, UK, EU, and Japanese sizing standards.
| US Size ↕ | Inner Diameter (mm) ↕ | Inner Circumference (mm) ↕ | UK / AU ↕ | EU ↕ | Japan ↕ |
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Figures are industry-standard approximations compiled from multiple jewelry sizing references. Manufacturer sizing can vary by ±0.25 size depending on band width and metal.
If you'd rather skip the screen entirely, any of these three physical methods gets you within half a size — especially when you repeat the measurement twice and average the result.
Cut a thin, non-stretch strip of paper, wrap it snugly around the base of the finger, and mark where it overlaps. Lay it flat against a ruler and match the millimeter reading to the chart above.
Swap the paper for a piece of non-stretch string or dental floss. Wrap it around the finger, pinch the meeting point, then lay it flat on a ruler and cross-check the mm reading against the chart.
Already own a ring that fits well? Trace its inner edge onto paper, measure the widest point of the traced circle in millimeters, then match that inner diameter to the chart — or the tool above.
Prefer to watch rather than read? This short walkthrough covers the same at-home methods explained above.
Finger size fluctuates more than most people expect. Keep these variables in mind before finalizing an order — especially for engagement rings and gifts.
Cold fingers shrink up to half a size. Measure at room temperature, never right after being outside in the cold.
Fingers swell slightly through the day. Evening measurements tend to run about a quarter size larger than morning ones.
If your knuckle is noticeably wider than the base of your finger, size for the knuckle and expect a slightly looser fit at the base.
Wider bands (8mm+) sit tighter than thin bands. Many jewelers recommend sizing up a quarter size for anything over 6mm.
Every conversion figure on this page is cross-referenced against multiple published jewelry-industry sizing standards and reviewed by our in-house jewelry specialist panel. Digital tools like the one above are estimation aids — screen calibration accuracy depends on your device's display and your own careful measurement. For high-value purchases, we always recommend a final check with a physical jeweler's ring sizer before ordering.
More in-depth guides on ring sizing, fit, and buying — from the same team behind this calculator.
The most accurate at-home method combines two approaches: measure with a non-stretch string or paper strip for circumference, then confirm with the inner-diameter trace of a ring that already fits. Cross-checking two methods against the chart above reduces the margin of error to roughly a quarter size.
Only if your printer is set to 100% scale with no "fit to page" option enabled — otherwise the millimeter markings shrink or stretch. Our on-screen calibration tool avoids this problem entirely by using a real card you already own as the reference object.
Yes. Each region uses a different numbering or lettering system, but they all map to the same underlying inner circumference in millimeters. The chart above converts between all five major standards using that shared measurement.
Generally yes. Bands wider than 6mm reduce the flexibility of the metal against your knuckle, so most jewelers recommend going up a quarter to half a size compared to a thin band.
Late afternoon or evening is best, since fingers are at their most "average" size after a full day of normal activity. Avoid measuring right after exercise, in cold weather, or first thing in the morning.
Cold temperatures can shrink fingers by up to half a ring size due to reduced blood flow. Always measure at normal room temperature for the most reliable result.
Guidance only — confirm with our free calculator for an exact fit.