On-screen ring sizer
Measure a ring size directly on your screen. First calibrate with any bank card so the display renders at true physical size, then measure a ring you own or try sizes against your finger.
Step 1, Calibrate your screen
Hold a real object of known size against the screen and adjust the slider until the outline matches it exactly. A bank card is easiest (they’re the same size worldwide), or use a common coin. This teaches the tool your screen’s real scale.
Tip: this works best on a phone or tablet. Make sure browser zoom is at 100%. Switch references above to double-check the scale.
How it works
Screens differ in physical size, so a circle drawn at “17 mm” isn’t really 17 mm until the screen is calibrated. A bank card is the perfect ruler because the ID-1 standard fixes every card at 85.60 mm × 53.98 mm worldwide. Match the outline to your card once and everything after that renders true to size.
Two ways to measure
- Measure a ring, lay a ring you already own on the screen and grow the circle until it sits inside the band.
- Try a size, pick a size and rest your finger over the circle to feel the fit.
No ring and no card handy? Use the string or paper method instead, or print a paper sizer.
Frequently asked questions
How accurate is an on-screen ring sizer?
Once calibrated against a standard bank card, it is accurate to within about a quarter of a size, good enough to shop confidently. For a custom or engagement ring, confirm the final size with a jeweller.
Why do I need a credit or bank card to calibrate?
Every ID-1 bank card in the world is exactly 85.60 mm wide. Matching the on-screen outline to a real card tells the tool your screen’s true scale, which differs between phones, tablets and monitors.
Does it work on a laptop or desktop?
Yes, but phones and tablets are easier because you can press the ring flat against the glass. On a desktop, hold the card and ring against the monitor and keep browser zoom at 100%.
Is my calibration saved?
Yes, it is stored locally in your browser only, so next time you open the sizer it remembers your screen. Nothing is uploaded.