ActualRingSize was engineered to solve the single biggest problem in online fine jewelry and watch shopping: uncalibrated, guesswork sizing charts that ignore your screen’s physical pixel density.
Operating systems and browsers report CSS pixels at an arbitrary 96 DPI—not true physical millimeters. By aligning our on-screen reference frame to a standard payment or ID card (85.60 × 53.98 mm), we compute your display’s exact physical pixels-per-millimeter ratio in real time.
Every ring conversion is computed deterministically from internal bore diameter ($d$) and inner circumference ($C = \pi \times d$) across US/Canada, UK Wheatsheaf (A–Z), European ISO 8653, Japanese (JJA), Indian, Swiss, Cartier, and Tiffany & Co. sizing scales.
All optical calculations, band-width comfort adjustments, watch lug-to-lug overhang projections, and GIA diamond carat dimensions run locally in your browser. Your physical measurements never leave your device.
Most web-based ring sizers assume a fixed screen resolution or ask users to print a PDF that silently scales to 94% ("Fit to Printable Area") in printer dialogs. Even a 0.40 mm error in inner diameter shifts a ring by a full half-size in the US/Canadian system—turning a comfortable fit into a ring that spins or refuses to pass the knuckle.
ActualRingSize eliminates printer scaling errors by turning your smartphone, tablet, or desktop monitor into a calibrated optical comparator. Once calibrated, our SVG reticle locks its stroke geometry so you align the inner edge of the physical ring against the outer edge of the measurement circle, preventing line-thickness parallax.
Physical display scale is only valid for your current browser zoom level and monitor viewport. If you zoom the page or drag your browser window onto a secondary external monitor, a saved pixel-per-millimeter value would silently produce inaccurate readings. That is why ActualRingSize keeps calibration in active page memory and automatically invalidates it if your viewport or display geometry changes.