About Ring Sizing
Ring shopping across borders — or surprise-gift shopping across a partner's jewelry box — runs into three incompatible labels for the same finger: a US 7, a UK N½, and an EU 54 are the same ring. The confusion is pure convention; underneath is one number in millimeters.
Convert from any starting point: the US size on a receipt, a diameter measured across an existing ring, or a circumference from a string test. You get all systems plus the physical measurements — the part worth writing down for future purchases.
The other sizing puzzle — feet — lives in the Shoe Size Converter.
How the Systems Relate
One measurement, three labels:
Diameter (mm) = 11.63 + 0.8128 × US size Circumference (mm) = π × diameter EU / ISO size = circumference in mm (that's the whole system) UK letters ≈ circumference alphabet (A ≈ 37.8 mm, ~1.25 mm per letter)
Worked example: US 7 → 17.3 mm diameter → 54.4 mm circumference → EU 54, UK N½. The EU system's honesty is worth copying: it just says the measurement.
Ring Size Chart
The common range — every row computed by this calculator's formulas:
| US | Diameter | Circumference | EU/ISO | UK |
|---|---|---|---|---|
| 4 | 14.9 mm | 46.8 mm | 47 | H |
| 5 | 15.7 mm | 49.3 mm | 49 | J½ |
| 6 | 16.5 mm | 51.9 mm | 52 | L½ |
| 7 | 17.3 mm | 54.4 mm | 54 | N½ |
| 8 | 18.1 mm | 57.0 mm | 57 | P½ |
| 9 | 18.9 mm | 59.5 mm | 60 | R½ |
| 10 | 19.8 mm | 62.1 mm | 62 | T½ |
| 11 | 20.6 mm | 64.6 mm | 65 | V½ |
UK letters between brands drift by a half step — when a letter matters (UK purchase), confirm against the mm circumference, which never lies.
Measuring Without a Jeweler
Two reliable home methods, in order of trustworthiness:
- Existing ring + ruler: measure the INSIDE diameter edge-to-edge in mm and enter it above — the best method, since the ring already fits.
- String or paper strip: wrap snugly where the ring sits, mark the overlap, measure the length in mm — that's the circumference (enter directly). Repeat twice; string stretch causes overshoot.
- Measure in the evening — fingers run smaller in the morning and in cold; knuckle-dominant fingers should size to pass the knuckle comfortably.
- Between sizes: go up for wide bands (they wear tighter), stay true for thin bands.
- Surprise shopping: borrow a ring she wears on the SAME finger of the same hand — other fingers differ by multiple sizes.
Free jeweler sizing exists almost everywhere — use it before resizing anything sentimental; resizing has limits, especially with stones around the band.