Ring Size Calculator
Find your ring size from a finger measurement or a ring that fits, in US, UK, EU and Japanese sizes. Free, no sign-up, and it runs in your browser.
Dedicated page: /en/ring-size-calculator
Estimate only, not a jeweller's sizing. For an engagement ring or anything that cannot be resized, confirm with a jeweller before ordering. Sizes vary by up to half a size between brands.
Wrap a strip of paper around the base of the finger, mark the overlap, and measure it in millimetres.
Wide bands fit tighter, so jewellers usually go up a quarter to half a size.
The ring has to pass the knuckle every day, so size to the knuckle when it is wider.
Measure at the end of the day, when fingers are warm and at their largest. Measure 3 times and take the middle value.
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Quick answer
A ring size calculator turns a finger measurement into your ring size. Wrap a paper strip around the finger base and measure it in millimetres, or measure a ring that fits across the inside. A 54.4 mm circumference is a US 7, which is 17.3 mm across, UK N and a half, EU 54, and Japanese 14.
About this Ring Size Calculator
Find your ring size from a finger measurement or a ring that fits, in US, UK, EU and Japanese sizes. It is one of the Health and Family on ToolUstad, and like every tool here it runs entirely in your browser: nothing you type, paste or open is uploaded to a server, and there is no sign-up or usage limit.
What is a ring size calculator?
A ring size calculator answers one question before you order a ring online: what size is this finger? A ring size is really a measure of the inside of the ring, its inner circumference or diameter in millimetres. There are three ways to get that number. Wrap a strip of paper around the base of the finger, mark the overlap, and measure the length: that is the circumference. Measure the inside diameter of a ring that already fits, straight across the centre from inside edge to inside edge. Or enter a US size you already know, and see what it is called everywhere else.
US ring sizes are a linear scale defined against the inside circumference: US size equals the circumference in millimetres minus 36.5, divided by 2.55. Each whole size is 2.55 mm of circumference, about 0.81 mm of diameter. A 54.4 mm finger gives 54.4 minus 36.5, divided by 2.55, which is 7.02, rounded to the nearest quarter size, US 7.
How to measure at home
Use paper, not string. Thread and yarn stretch several millimetres under tension and will read small. Cut a strip about 10 mm wide and 100 mm long, wrap it around the base of the finger where the ring will sit, pull it snug, touching the skin all the way round but not digging in, and mark where the end meets the rest of the strip with a fine pen. Lay the strip flat and measure from the end to the mark in millimetres. Three details decide whether the number is trustworthy.
When to measure, and the wide-band rule
Best practices
- Measure in the evening, three times: take the middle value, on the finger and hand the ring will live on.
- Confirm before anything that cannot be resized: eternity bands, tungsten, titanium and tension-set rings generally cannot be resized at all.
Common mistakes to avoid
- Measuring with string, which stretches and reads small, or measuring on a cold morning, which reads small too.
- Ordering a wide band in your thin-band size: it will feel half a size tighter than the number suggests.
Who is the ring size calculator for?
Anyone ordering a ring online, anyone sizing a surprise gift from a ring that already fits, and anyone checking what their US size is called in the UK, Europe or Japan before buying abroad.
Related terms: ring size chart, how to measure ring size, US to UK ring size, EU ring size, printable ring sizer, ring size conversion, wide band ring size.
Estimate only, not a jeweller's sizing. For an engagement ring or anything that cannot be resized, confirm with a jeweller before ordering.
Learn: how to use the Ring Size Calculator
- Pick what you measured: finger circumference with a paper strip, the inside diameter of a ring that fits, or a US size you already know.
- Enter the number in millimetres, centimetres or inches.
- Read your size in all four systems, and the wide-band adjustment if your band is 6 mm or wider.
Features
- Three ways in: circumference, diameter, or a known US size
- US size to the nearest quarter, by the standard formula
- UK, EU (ISO 8653) and Japanese conversions in one view
- Wide-band adjustment of half a size
- Knuckle note for fingers wider at the knuckle
- Full conversion chart, US 3 to 13 in half sizes
- Printable sizer guide with a 50 mm calibration bar
Worked example
A paper strip around the finger measures 54.4 mm. The formula is (54.4 minus 36.5) divided by 2.55, which is 7.02, so the size is US 7. That is 17.3 mm inside diameter, UK N and a half, EU 54, and Japanese 14. For a wide band 6 mm or wider, order US 7 and a half instead.
Frequently asked questions
How do I measure my ring size with string or paper?
Cut a strip of paper about 10 mm wide and 100 mm long, paper not string, because thread stretches. Wrap it snugly around the base of the finger, mark where it overlaps, lay it flat and measure to the mark in millimetres. That length is the finger circumference.
How accurate is the string method?
To about a quarter size, if you use a non-stretchy strip, pull it snug but not tight, and measure the mark to 0.5 mm. Measure three times and take the middle value. For an expensive ring, a two-dollar plastic ring sizer beats any home method.
Should I size up for a wide band?
Usually yes. Bands wider than about 6 mm contact more skin and fit tighter, so jewellers usually recommend a quarter to half size up. For bands 8 mm or wider, go up a full size. If you are between sizes anyway, take the larger.
Why do my fingers measure different sizes on different days?
Fingers swell with heat, salt, time of day and exercise, by up to half a US size between a cold morning and a warm evening. Measure at the end of the day at room temperature, and size the finger the ring will actually live on.
What if my knuckle is wider than my finger?
Size to the knuckle: the ring has to pass it every day, and a slightly loose fit at the base beats a ring that will not go on. Some jewellers fit a quarter size down from the knuckle measurement so the ring does not spin.
Can I measure a ring instead of the finger?
Yes. Lay a ring that fits flat and measure straight across the inside, edge to edge, to the nearest half millimetre. That is the inside diameter, and the calculator multiplies it by pi for the circumference.
Is my ring size the same in every country?
The finger is, the numbering is not. US 7 is UK N and a half, EU 54 and JP 14: the same physical ring, four labels.
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