How to measure your ring size at home

1. Why screen calibration comes first

One of the most common complaints about ring sizer apps is "isn't accurate on my phone." The cause is that every phone screen has a different pixel density (PPI), so a circle drawn at, say, a 100px radius shows up at a different real-world size on different phones.

Fixing that requires a real, fixed-size reference. A bank card, ID card, or transit card follows the international ID-1 standard (85.6mm × 53.98mm), is easy to find, and is always the same size, which makes it a good calibration reference. Matching an on-screen rectangle to the card once makes every shape on that screen accurate in real millimeters from then on. No camera scanning of the card happens — you just hold it up to the screen and match it by eye.

2. Why you measure the ring's inner edge

Ring size is defined by the inner diameter (or inner circumference) that actually touches your finger — not the ring's outer edge or its band width. So when you match the on-screen circle to the ring, line it up with the inner edge of the ring's hole.

• Lay the ring flat, or hold it steady in your hand
• Adjust the on-screen circle's size with the slider to match the inner edge of the ring's hole
• Fine-tune in 0.1mm steps until the circle's edge and the ring's inner edge line up exactly
• Save the result — it shows across multiple sizing systems at once

3. Why there are so many sizing systems

The same ring is labeled differently depending on the country: Korea uses 호수 (a numbered scale), US/Canada uses numbers with half sizes, UK/Australia uses letters, the EU uses circumference in millimeters, Japan has its own numbered scale, and Switzerland uses its own notation too. As a reference point, an inner diameter of about 17.3mm is roughly US size 7, about 54.4mm in circumference, Korean size 14, and UK size N½ (diameter × π ≈ circumference: 17.3 × 3.14159 ≈ 54.3mm, close enough).

Once you measure your ring size accurately a single time, you can convert it to whichever system a given store uses, whether you're buying locally or importing from another country.

4. Tips for a more accurate measurement

Fingers are slightly larger in the evening or in warm weather due to natural swelling, so measuring during the daytime at a normal temperature gets you closer to your true size.

If you're between two sizes, size up — especially for a wide band. Wide bands feel tighter than thin ones at the same inner diameter.

Measure 2-3 times rather than once, and use whichever result comes up most consistently.

For an expensive or custom-made ring, treat a Ringmate measurement as a strong reference point, and confirm the final size with a professional jeweler before ordering.

5. How to do it in Ringmate

Open Ringmate, calibrate your screen once with a card, then use ring-measuring mode to match the circle to the ring's inner edge. The result shows US/Canada, UK/Australia, EU, Japan, Korea and Switzerland sizes plus the raw inner diameter in mm, all on one screen, and you can save it by person, hand and finger. There's no account and no limit on how many times you can re-measure.