Ring sizing, made simple
The perfect proposal starts with the perfect fit.
Find a ring size in seconds, convert US, UK and EU sizes, and measure at home with confidence. Sizes are calculated with the math shown; everything else links to a public source with the date we checked it.
Ring size finder
Choose what you know. The conversions update as you type.
Diameter and circumference are calculated from the US/Canada formula (each whole size adds 0.8128 mm of inside diameter).[1 · Oct 29, 2026] UK letters come from GIA's chart,[2 · Oct 29, 2026] and the ISO/EU size is the inside circumference in mm.[1 · Oct 29, 2026] Between two sizes, GIA and Jewelers Mutual suggest the larger one.[2 3 · Oct 29, 2026] Charts vary slightly by jeweler, so confirm with a jeweler's finger gauge for an important purchase.
- Math shown for every calculated size
- Dated source links beside every figure
- US, UK, EU and more, side by side
Ring size guides
- Ring size chartUS sizes 3 to 13 with inside diameter and circumference in mm and inches.
- Measure at homeString, paper strip or a ring that already fits, with a circumference table.
- Size conversionUS to UK letters, ISO/EU, Italy, Spain and Germany.
- Wide bands and resizingWhen to size up, and which styles are hard to resize.
Planning a surprise?
Find their size secretly
- Borrow a ring that already fits the same finger. Measure across the inside, edge to edge, in millimetres. That is the inside diameter: type it into the size finder or compare it with the chart.
- Check which hand it came from. GIA says that for a right-handed person the left ring finger is typically about half a size smaller than the right.[2 · Oct 29, 2026]
- Between two sizes, go larger. GIA and Jewelers Mutual both suggest it;[2 3 · Oct 29, 2026] GIA notes it is easier to remove metal than add it.[2 · Oct 29, 2026]
- Mind the band width. Wider bands fit more snugly; Brilliant Earth suggests at least a half size up for bands over 4 mm.[4 · Oct 29, 2026]
At home, step by step
How to measure ring size
1 Cut a strip
Cut a piece of string about 6 inches long, or a paper strip about 6 in × 1/4 in.[3 · Oct 29, 2026]
2 Wrap and mark
Wrap it snugly around the base of the finger, below the knuckle, and mark where it overlaps.[3 · Oct 29, 2026] Check that it slides over the knuckle; if the knuckle is noticeably larger, Brilliant Earth suggests a size between the two measurements.[4 · Oct 29, 2026]
3 Measure in millimetres
Lay the strip flat and measure to your mark. That length is the inner circumference; enter it in the size finder, or divide by π for the diameter.
4 Repeat on different days
Measure three times on different days; Jewelers Mutual recommends this because finger size changes.[3 · Oct 29, 2026]
GIA cautions that string can stretch, paper can curl, and neither accounts for the knuckle, so treat a home result as an estimate; a jeweler's finger gauge is the most accurate option.[2 · Oct 29, 2026] Fingers shrink in the cold and swell in heat,[2 · Oct 29, 2026] and Jewelers Mutual suggests measuring midday.[3 · Oct 29, 2026] Full measuring guide
Ring size conversion chart
Whole US sizes. Half sizes and Italy/Spain sizes are in the full conversion chart.
| US / Canada | UK / Australia | EU / ISO | Inside diameter | Inside circumference |
|---|---|---|---|---|
| 3 | F | 44 | 14.07 mm | 44.2 mm |
| 4 | H | 47 | 14.88 mm | 46.8 mm |
| 5 | J | 49 | 15.69 mm | 49.3 mm |
| 6 | L | 52 | 16.51 mm | 51.9 mm |
| 7 | N | 54 | 17.32 mm | 54.4 mm |
| 8 | P | 57 | 18.13 mm | 57.0 mm |
| 9 | R | 60 | 18.95 mm | 59.5 mm |
| 10 | T | 62 | 19.76 mm | 62.1 mm |
| 11 | V | 65 | 20.57 mm | 64.6 mm |
| 12 | X | 67 | 21.38 mm | 67.2 mm |
| 13 | Z½ | 70 | 22.20 mm | 69.7 mm |
Diameter and circumference: our arithmetic from the US/Canada formula, d = 11.63 + 0.8128 × size and C = π × d.[1 · Oct 29, 2026] UK letters from GIA's international chart.[2 · Oct 29, 2026] ISO/EU = circumference rounded to a whole mm.[1 · Oct 29, 2026]
Comfort fit
Wide bands and between sizes
- GIA says wide shanks need a slightly larger size.[2 · Oct 29, 2026]
- Brilliant Earth suggests at least a half size up for bands wider than 4 mm,[4 · Oct 29, 2026] and Jewelers Mutual also recommends a size up for wider bands.[3 · Oct 29, 2026]
- Pavé, channel-set and eternity rings are difficult to resize because stones run around the band, GIA notes,[2 · Oct 29, 2026] so measure carefully more than once before ordering those styles.
Before you buy
Shop with confidence
- Check the seller's own size chart and resizing policy; charts from different jewelers can differ by a fraction of a size because of rounding.
- When ordering from another country, give the seller your measurement in millimetres as well as the size.
- For an important purchase, confirm the size with a jeweler's finger gauge.[2 · Oct 29, 2026]
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Sources: 1. Wikipedia, Ring size. 2. GIA 4Cs, How to determine ring size. 3. Jewelers Mutual, How to measure ring size. 4. Brilliant Earth, How to measure ring size. Checked Oct 29, 2026.