Ring Size Calculator
Place a ring you already own on your screen to measure ring size exactly — no printing required.
Calibrate Your Screen
Hold a physical credit card against your screen and drag the slider until the outline below matches it exactly.
How this ring size calculator works
Every screen has a different pixel density, so a circle that measures 17 mm on one laptop can measure 20 mm on another. This tool solves that by calibrating first: you resize an on-screen rectangle until it matches a standard credit card, which is 85.60 mm wide worldwide. That gives an exact pixels-per-millimetre ratio for your specific display.
You then resize a circle until it matches the inside edge of your ring — the hole your finger passes through, not the outer edge. The tool converts that diameter into US, UK, EU and Indian ring sizes at once and saves the result to your device.
Tips for an accurate measurement
- Use a ring that fits the finger you actually intend to wear the new ring on.
- Set your browser zoom to 100% before calibrating, or the ratio will be wrong.
- Measure the inner diameter of the band, not the outer diameter.
- If you land between two sizes, choose the larger one.
- For bands wider than 6 mm, add half a size.
No ring to measure? The Camera Sizer measures your finger directly. You can also compare your result against the full ring size chart or read our complete guide to how to measure ring size at home.