A ring you have. A size to start with.
Calibrate with a standard bank card, then place an existing round ring flat on the screen. Adjust the circle until its outer edge just meets the inside opening of the ring. Look straight down rather than at an angle. The number is the closest approximate US size from our reference chart.
Start with the right scale
A webpage cannot reliably know your screen’s physical size. Match the two calibration lines to the short edge of a standard bank card (53.98 mm). Use the middle of each line as the endpoint. No card photo, card details or camera permission is needed. An unusually sized card gives the wrong scale.
We keep calibration in this page’s memory only. Reloading, rotating, pinch zooming or changing the screen scale requires calibration again. Some monitor changes cannot be detected, so recalibrate if you move this window to another display. The fine controls help positioning; they are not a claim of measurement accuracy.
Measure the ring, not the finger
Use a ring that already fits the intended finger, with a round opening and an edge that can sit flat against the display. Wide, oval, open or shaped rings need a different assessment. Another ring of the same nominal size may fit differently. Check again by rotating and repositioning the reference ring, then making a fresh match.
Where the sizes come from
The US half-size estimates use the published inside-diameter table in Tiffany & Co.’s size guide, covering sizes 3–13. Diameter values are rounded, and retailer charts can differ. We show the nearest size and neighboring sizes when the measurement is between chart values. There is no extrapolated size outside that table.
GIA’s sizing guidance explains why ring shape and construction matter. Confirm an important purchase with a jeweler or physical sizing gauge and the seller’s chart. Smart rings may use their own sizing system.
Keyboard and privacy
Use Tab to reach the sliders and buttons. Arrow keys adjust the focused slider; − and + make fine adjustments. Calibration and measurements stay in page memory and are cleared when you leave. General site analytics are described on Privacy.
More tools: Online ruler · Photo protractor