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
Grab any bank, credit or ID card (they’re all the same size worldwide). Hold it against the screen and use the slider until the outline matches your card exactly. 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%.
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.