Free tool
Ring sizer at actual size
Match a card
Hold a bank card, ID or loyalty card flat against the screen. Slide until the outline matches its edges.
Screen matched on this device.
Match your ring
Lay a ring that fits on the circle. Slide until the circle just fills the inside of the band.
How this sizer works
Screens pack pixels at different densities, so a web page cannot know how big a millimeter is on yours. A card fixes that. Bank cards and many driver's licenses and ID cards share the ID-1 size from ISO/IEC 7810, 85.60 by 53.98 mm. Once the outline matches your card, the page knows how many pixels make a millimeter on this screen and saves that number in this browser. Nothing is sent anywhere.
The circle then shows a true inside diameter. Each US size adds 0.032 inches, or 0.81 mm, so a miss of 0.4 mm is half a size. UK letters follow British Standard 6820 at 1.25 mm of circumference per letter, and the EU size is the inside circumference in millimeters. The ring size chart lists every conversion, including Japanese and Swiss sizes.
Getting an accurate reading
- Use a ring from the same finger. The left ring finger is typically about half a size smaller than the right for right handed people, per GIA.
- Match the inside edge of the band, not the outside, and look straight down at the screen.
- Keep the page at its normal zoom. If you zoom in or move to another screen, match the card again.
- Wide bands fit more snugly than thin ones, so GIA suggests a bit more room for them.
- Treat the result as a starting point and have a jeweler confirm it before you buy.
A ring size app on your iPhone
The DreamRing app for iPhone has a ring sizer too. Lay a ring you already wear on an on-screen circle, lay your finger across the screen, or measure a strip of paper against an on-screen ruler. Those sizes are approximate as well, so a jeweler should confirm before you order.