for a ring you already own

💍 Ring Size Finder

Figure out a ring's size two ways: type in a measurement you already took, or measure it right on your screen using nothing but a credit card and the ring itself. Everything runs in your browser — nothing is uploaded anywhere.

1Enter a measurement
How to measure a ring you already have
Lay the ring flat and measure straight across the inside of the hole, at its widest point, with a ruler or calipers — that's the diameter. Or wrap a thin strip of paper around the inside of the band, mark where it overlaps, then measure that length flat — that's the circumference. Worn rings are often slightly oval; if so, measure twice at a right angle and average the two.
millimeters
2No ruler handy? Measure on screen instead

This calibrates against a standard credit/debit/ID card, then lets you size the ring directly against your screen — accurate regardless of your screen's resolution or zoom level, since it measures against the real card rather than assuming a pixel density.

2aCalibrate with a card
200 px

Hold a card up to the screen against the short edge (works on phones too) and drag until the box matches it exactly. Use arrow keys after clicking the slider for 1px nudges, or Shift+arrow for bigger jumps.

Not calibrated yet.
2bMatch the ring
17.00 mm

Lay the ring on the screen over the circle and adjust until its inner edge lines up. Calibrate step 2a first.

Result
Enter a measurement above to see sizes.