100% Free & Private: Measure instantly on screen in MM, CM, and Inches — No download needed.
Free online ring sizer,
calibrated to your screen
Work out your ring size without a ring sizer: hold a bank card against your screen to calibrate it to real millimetres, then measure a ring you already own — or your finger with a strip of paper. Nothing is uploaded.
Four ring size sites give three different UK answers for US 6. Every number here is computed from the published standard instead. See the arithmetic →
Prerequisite: Any standard bank card — every one is 85.60 × 53.98 mm (ISO/IEC 7810), which is what makes this accurate. A ring that already fits helps; a strip of paper works just as well.
Online Measurement
What is my ring size?
Measure a ring on screen, or type a measurement you already have. The calculator converts between diameter and circumference in millimetres, centimetres and inches, and gives you every national size at once.
Interactive ring sizer
Calibrate Screen Scale
Hold any standard bank card upright against your screen and adjust the slider until the outline matches its exact width (53.98 mm).
Hold a bank card against the screen and line its short edge up between the two bars
53.98 mm
1:1 Physical Scale Outline
Inside Diameter
Your Size Is
Why UK and India can differ from your jeweller’s chart
Published UK letter charts vary by up to half a size, because British scales do not all include the same half letters. Ours follows BS EN 28653 exactly. If your jeweller uses a different chart, give them the circumference in millimetres above instead.
India has no official ring size standard. Four Indian jewellers we checked number rings by inner circumference in millimetres minus 40, and that is what we show. Tanishq publishes a chart that runs about one size smaller. Give your jeweller the diameter in millimetres - that number is unambiguous.
About the tool
How this ring sizer works
Most online ring sizers ask you to hold a ring against a picture on your screen. That cannot work, and the reason is simple arithmetic: a screen has no fixed relationship between pixels and millimetres. The same image is physically larger on a 24-inch monitor than on a laptop, larger again on a 4K display running at a different scaling factor, and different once more if your browser is zoomed to 110%. An image that is correct on the developer's machine is wrong on almost everyone else's, and nothing on the page tells the visitor that it is wrong.
Calibrating against a bank card
This ring size calculator solves that before it measures anything. Every payment card in the world is manufactured to ISO/IEC 7810 ID-1: 85.60 × 53.98 mm, to a tolerance of a tenth of a millimetre. Bank cards, credit cards, most driving licences and most national ID cards are all the same object dimensionally. So you hold one against the screen, drag the slider until the outline matches its edges, and the tool now knows exactly how many pixels your display puts in a millimetre — on a standard 96 DPI screen that is about 204 pixels across the card, but the point is that it no longer has to assume.
That number is saved in your browser, so you calibrate once. Everything the tool draws afterwards — the ring circle, the millimetre grid behind it, the 10 mm scale bar — is scaled from it. If you change screens or zoom level, recalibrate and everything moves with you.
Three ways to give it a measurement
Once calibrated, the virtual ring sizer takes whatever you have:
- A ring that already fits. Lay it on the circle and match the circle to the ring's inside edge. This is the most accurate route, because a ring is rigid and a finger is not.
- A finger you have measured. Wrap a strip of paper round the base of the finger, mark the overlap, measure it flat, and type that in as a circumference.
- A number from somewhere else. A jeweller's reading, a caliper, a size printed inside an old band — type it straight into the field.
The two switchers above the readout are deliberately separate. One askswhat you measured — inside diameter or inside circumference — and the other askswhich unit you want, millimetres, centimetres or inches. Those are independent questions, and putting them in one row of buttons, as this tool once did, quietly makes some combinations unreachable. If your ruler is marked in inches and you measured around the finger, that combination exists here.
What the conversions are built from
Every size shown is computed from the published standard for that country, not copied from another site's chart. EU sizes come from ISO 8653, where the size is the inner circumference in millimetres, defined from 41 to 76. Japan comes from JIS S 4700, which runs 1 to 35. UK letters come fromBS EN 28653, one letter per 1.25 mm of circumference. The US scale has no governing standard at all — it is a trade convention, and we say so rather than implying otherwise.
This matters more than it sounds. Because the numbers are computed rather than transcribed, no two readings on this site can disagree with each other, and the tool cannot drift from the chart. Run the same diameter through diameter mode, circumference mode, centimetres and inches and you get the same size every time — which is not true of every ring sizer chart published, including some by very large jewellers.
The slider covers 12.89 mm to 24.35 mm of inner diameter, which is the exact band where all seven systems answer. Beyond it, sizes stop being defined — and where a scale does not define a size, this tool prints an em dash instead of inventing one.
How accurate is it, honestly
The arithmetic is exact; your hands are not. A full US size is 0.81 mm of diameter and a quarter size is 0.2032 mm — small enough that a slightly sloppy calibration, a ring sitting at an angle on the glass, or a paper strip pulled half a millimetre tight will move the answer. Measure twice. Where the result falls between two sizes, and the ring is a gift or cannot be resized, take it to a jeweller with a steel mandrel; that is the one thing no screen can replace.
Fingers also change through the day — heat, salt and exercise swell them, cold shrinks them, and the swing across a single day is easily half a size. Measure in the evening at normal room temperature, on the hand the ring will actually be worn on.
Free, and nothing leaves your browser
There is no account, no email gate and no PDF to download. The whole ring sizer tool runs as JavaScript on this page: your measurement is never sent anywhere, because there is nowhere for it to be sent. The only thing stored is your screen's calibration, kept in your own browser so you do not have to redo it, and removable by clearing this site's data.
If you would rather work on paper, theprintable ring sizerprints a paper gauge with a scale-check square, so you can prove your printer did not shrink the page — the failure that makes most printable sizers quietly wrong. For the full conversion tables see thering size chart, and for step-by-step instructions there is a guide tomeasuring your ring size at home.
Finger size context
Is your size normal?
Almost certainly. Rings are sold from about US 3 to US 13, and most adults sit in a narrow band inside that — commonly quoted as US 6 for women and US 9 for men.
Worth stating plainly: those two figures are not standardised and there is no census of finger sizes. They describe what jewellers sell, not what people have.
Step-by-step
Two ways to measure
If you have a ring that already fits, lay it on the circle above and size the circle until its outer edge meets the inside of the band — the metal itself is not part of the measurement. If you do not, wrap a strip of paper round the base of the finger, mark the overlap, and type the flat length in as a circumference.
Avoid string — it stretches, and it stretches in the direction that makes your finger read a size too small.
Conversion reference
Ring size conversion chart
Computed directly from ISO 8653, BS EN 28653, and JIS S 4700 standards.
| US / CA | UK / AU | EU / ISO | Japan | India | Dia (MM) | Dia (CM) | Dia (In) | Circ (MM) |
|---|---|---|---|---|---|---|---|---|
| 3 | F½ | 44 | 4 | 4 | 14.07 mm | 1.407 cm | 0.554 in | 44.21 mm |
| 3½ | G½ | 45 | 5 | 5 | 14.48 mm | 1.448 cm | 0.570 in | 45.48 mm |
| 4 | H½ | 47 | 7 | 7 | 14.88 mm | 1.488 cm | 0.586 in | 46.76 mm |
| 4½ | I½ | 48 | 8 | 8 | 15.29 mm | 1.529 cm | 0.602 in | 48.04 mm |
| 5 | J½ | 49 | 9 | 9 | 15.70 mm | 1.570 cm | 0.618 in | 49.31 mm |
| 5½ | K½ | 51 | 10 | 11 | 16.10 mm | 1.610 cm | 0.634 in | 50.59 mm |
| 6 | L½ | 52 | 12 | 12 | 16.51 mm | 1.651 cm | 0.650 in | 51.87 mm |
| 6½ | M½ | 53 | 13 | 13 | 16.92 mm | 1.692 cm | 0.666 in | 53.14 mm |
| 7 | N½ | 54 | 14 | 14 | 17.32 mm | 1.732 cm | 0.682 in | 54.42 mm |
| 7½ | O½ | 56 | 15 | 16 | 17.73 mm | 1.773 cm | 0.698 in | 55.70 mm |
| 8 | P½ | 57 | 16 | 17 | 18.14 mm | 1.814 cm | 0.714 in | 56.97 mm |
| 8½ | Q½ | 58 | 18 | 18 | 18.54 mm | 1.854 cm | 0.730 in | 58.25 mm |
| 9 | R½ | 60 | 19 | 20 | 18.95 mm | 1.895 cm | 0.746 in | 59.53 mm |
| 9½ | S½ | 61 | 20 | 21 | 19.35 mm | 1.935 cm | 0.762 in | 60.80 mm |
| 10 | T½ | 62 | 21 | 22 | 19.76 mm | 1.976 cm | 0.778 in | 62.08 mm |
| 10½ | U½ | 63 | 23 | 23 | 20.17 mm | 2.017 cm | 0.794 in | 63.36 mm |
| 11 | V½ | 65 | 24 | 25 | 20.57 mm | 2.057 cm | 0.810 in | 64.64 mm |
| 11½ | W½ | 66 | 25 | 26 | 20.98 mm | 2.098 cm | 0.826 in | 65.91 mm |
| 12 | Y | 67 | 26 | 27 | 21.39 mm | 2.139 cm | 0.842 in | 67.19 mm |
| 12½ | Z | 68 | 27 | 28 | 21.79 mm | 2.179 cm | 0.858 in | 68.47 mm |
| 13 | Z+1 | 70 | 29 | 30 | 22.20 mm | 2.220 cm | 0.874 in | 69.74 mm |
UK sizes run as long stretches of half sizes. That is correct, not a bug: a US step is 2.55 mm of circumference and a UK step is 1.25 mm, so the two scales never line up. * Computed strictly from ISO 8653:2016, BS EN 28653:1993, and JIS S 4700:2022 standards. 1 Inch = 25.40 mm.
Deep dive
Why two ring size charts give you different answers
Search for a conversion chart and you will find dozens of tables that contradict each other. For a US 6, four popular charts give three different UK sizes: some say L, some say L ½, some say M.
The discrepancy is real, and it is not an error in anyone’s math. It comes from three things that ring size pages almost never explain.
The UK standard doesn't say what you think it says
The British standard (BS EN 28653:1993, which identical to ISO 8653) defines size A as a 37.5 mm circumference, with every whole letter adding exactly1.25 mm of circumference. A US size 6 has an inner diameter of 16.51 mm, which gives a circumference of51.87 mm.
Subtract 37.5 from 51.87 and divide by 1.25, and you get 11.49 steps above A. Step 11 is L (51.25 mm); step 12 is M (52.50 mm). 11.49 landsdead in the middle, just 0.01 mm from L ½.
A chart that rounds down gives you L. A chart that rounds up gives you M. A chart that keeps half-sizes gives you L ½. None of those three charts is “wrong” — but a ring made to size M is 1.25 mm larger around the finger than a ring made to size L, and that is enough to turn a good fit into a ring that slips off over the knuckle.
India, France, Italy, Spain and Brazil are one scale
This is the part no other ring size page seems to say out loud. France, Italy, Spain, Switzerland and Brazil all number rings the same way: take the inner circumference in millimetres and subtract 40. Brazil’s standard, ABNT NBR 16058, is aligned to ISO 8653 and gives the same answer — the Brazilian trade rule is literally “add 40 to the size to get the perimeter”. So a French size 12, an Italian 12 and a Brazilian aro 12 are the same physical ring. Our table shows them in separate columns because that is what people search for, but the number will always match.
Where we are genuinely unsure: India
India has no sizing standard — there is no BIS specification for ring sizes, so there is nothing to be wrong about. What we did instead of copying somebody’s chart was compare the published tables of four Indian jewellers: Jewelove, RishiRich Jewels, Gems Mart Jewellers and Sukkhi. All four turn out to use the same “circumference minus 40” rule as France and Brazil, and they agree on every row they publish — Sukkhi’s table runs from size 1 to 37 and fits the rule exactly. That is what we compute.
The catch is Tanishq, the largest jeweller in India, whose published chart runs roughly one size smaller than that convention. We could not confirm the offset across their full range, because Tanishq blocks requests from Pakistan, where this site is built — so we are telling you what we know rather than papering over it. Every competitor we audited prints one Indian number as though it were settled. We print ours next to the diameter in millimetres, and that millimetre figure is the one to give your jeweller. It is the only unambiguous answer.
Edge cases
Cases the number alone won't cover
Your knuckle is wider than the base of your finger
Measure both, and take the size that clears the knuckle. A ring that fits the base perfectly but will not pass the knuckle is not wearable; a ring that clears the knuckle and sits a little loose is. If the gap between the two is more than about a full size, a jeweller can fit sizing beads inside the band — that solves it properly, and no calculator can.
The band is wide
A wide band covers more of the finger and feels tighter at the same diameter. The usual advice is to add a quarter to a half size above roughly 6 mm of width.
We will not dress that up as a calculation. There is no formula for it — the correction depends on how soft the finger is and how rounded the inside edge of the band is, and no standard covers either. Anyone giving you an exact figure for this has invented it. Try the half size up if the band is wide and the fit is borderline.
Fingers change size during the day
Warmth, salt, exercise and altitude all swell fingers; cold shrinks them. The swing is real enough to cross a half size, which is why a ring can spin in the morning and stick by evening. Measure at room temperature, in the middle of the day, and if you get two different answers, take the larger.
You are sizing someone else's finger, secretly
Borrow a ring they already wear on the right finger and measure it with method 1 above. The finger matters: a ring worn on the right hand is usually a quarter to a half size different from the same finger on the left, and non-ring fingers are not comparable at all. If you can only get a ring from the wrong finger, buy the ring resizable and size it after.
Some rings cannot be resized at all
Eternity rings set with stones the whole way round, tension settings, and rings in tungsten, titanium, ceramic or stainless steel are effectively fixed — there is no plain metal to cut and no safe way to work the material. For any of those, and for an engagement ring, confirm with a jeweller before you buy. An on-screen measurement is a good estimate; it is not a fitting.
FAQ
Questions people actually ask
Taken word for word from Google’s “People also ask”. Nothing here is invented to pad the page.
How can I measure my ring size at home?
Two ways, both on this page. If you own a ring that fits, calibrate your screen against a bank card, then size the on-screen circle until its outer edge meets the inside of the band. If you do not, wrap a strip of paper around the base of your finger, mark the overlap, measure the flat strip against a ruler and type the length in. Both give you an inner diameter, which is the only measurement ring sizes are actually built from.
Can I measure my ring size on my phone?
Yes, and a phone is often better than a laptop because you can hold the ring flat against the glass. Calibrate on the phone itself — screen scale differs between devices, so a calibration saved on your laptop will not be right here. Keep browser zoom at 100%.
Is there a virtual ring sizer?
This is one. A virtual ring sizer draws a circle on your screen at a known physical size so you can compare a real ring against it. The part that matters is calibration: without it the tool is guessing how large a millimetre is on your display, and the answer can be a full size out.
Is size 7 a large ring?
No. US 7 is an inner diameter of 17.32 mm and sits just above the most common women's size of 6 and below the most common men's size of 9. It is one of the most frequently sold sizes there is.
How can I find out my ring size?
Measure the inner diameter of a ring that already fits, or the circumference of the finger itself, then convert. Everything else — printable charts, string tricks, guessing from glove size — is a less direct route to the same two numbers. Diameter and circumference are locked together as circumference = π × diameter, so either one gives you the other exactly.
Can I size my ring at home?
You can measure at home accurately enough to buy most rings. You cannot resize one at home — that needs a jeweller's saw, solder and mandrel. If the ring is an engagement ring, or in tungsten, titanium, ceramic or steel, confirm the measurement with a jeweller before buying, because those cannot be altered afterwards.
Does ring size vary by finger?
Considerably. Every finger differs, and the same finger differs between hands — a ring worn on the right hand is commonly a quarter to a half size away from the left. Measure the exact finger the ring will live on. A measurement from any other finger is not transferable.
How can I tell my ring size without measuring?
You cannot, reliably. Estimates from height, glove size or shoe size are guesses, and the range they cover is wider than the whole sold size range. The closest thing to "without measuring" is borrowing a ring that already fits and comparing it to the circle on this page, which takes about a minute.
Can I measure my ring online?
Yes — this page does it entirely in your browser. Nothing is uploaded, no photo is taken and no account is needed. The calibration is stored only on your own device so a repeat visit skips that step.
Is there an app to check your ring size?
There are several, but you do not need to install anything. A browser page can measure exactly as accurately as an app, because both depend on the same thing: calibrating the screen against an object of known size. This page uses a bank card, which is 85.60 × 53.98 mm everywhere in the world under ISO/IEC 7810.
What is the most common ring size?
US 6 for women — an inner diameter of 16.51 mm — and US 9 for men. Most adult sizes fall between US 4 and US 13. Being outside that band is normal, it just narrows what is available off the shelf.
What is the best ring sizer to use?
A jeweller's steel ring gauge set is the most accurate thing there is, and it is what you should use for an engagement ring. For buying online, a calibrated on-screen sizer or a correctly printed paper sizer is close enough for a resizable ring. The main failure in every method is scale: an uncalibrated screen and a printer set to "fit to page" are both wrong in the same way.
Can I size my ring on my phone?
Yes. Open this page on the phone, calibrate against a bank card held flat on the screen, then lay the ring on the glass and size the circle to the inside of the band. Do not reuse a calibration from another device — pixel density differs, and that is exactly what calibration corrects for.
How do I know my correct ring size?
Measure more than once, on different days, and at room temperature. Fingers swell with heat, salt and exercise and shrink when cold, and the swing across a day can cross a half size. If two measurements disagree, take the larger — a slightly loose ring is wearable, a tight one is not.
Is a ring sizer universal?
The measurement is; the numbering is not. Inner diameter in millimetres means the same thing everywhere. The size label does not — US uses numbers, the UK uses letters, EU/ISO uses the circumference itself, and Japan uses its own scale. That is why this tool reports the diameter alongside every size: the millimetre figure is the one no jeweller can misread.
Is a size 7 ring big for a girl?
No. US 7 (17.32 mm inner diameter) is one step above the most common women's size of US 6 and well inside the ordinary range. Adult women's sizes commonly run from about US 4 to US 9.
How do I convert my finger diameter to ring size?
Multiply the diameter by π to get the circumference, then read off the scale you need. EU/ISO 8653 sizes are the circumference in millimetres; France, Italy, Spain, Brazil and most Indian jewellers use that number minus 40; the US scale is diameter in inches, where size 0 is 0.458 in and each size adds 0.032 in. The tool on this page does all of these at once from one diameter, which is why its outputs cannot contradict each other.
How to size a ring with a sizer?
With a set of graduated rings, slide each one on until you find the one that passes the knuckle with slight resistance and sits without spinning. With a mandrel, drop the ring over the cone and read the mark where it stops. With this page, match the on-screen circle to the inside of the ring — not the outside, which includes the metal.
Can I size a ring at home?
Measuring, yes. Physically resizing, no — home methods such as ring adjusters, tape or glue-in inserts change the fit but not the ring, and they can mark soft metals. Treat them as a temporary fix while you have the ring properly sized.
Which rings cannot be resized?
Eternity rings set with stones all the way round, tension settings, and anything made of tungsten, titanium, ceramic or stainless steel. There is no plain section of metal to cut and rejoin, and those materials cannot be worked the way gold or silver can. For any of them, get the size confirmed by a jeweller before ordering.
What is 7 inches in ring size?
Nothing — 7 inches is far too large for a finger, and anyone measuring that has almost certainly measured a wrist. A ring is roughly 2 inches around: US size 7 has an inner circumference of 2.14 in (54.42 mm) and an inner diameter of 0.68 in (17.32 mm). If you meant 7 inches of paper strip wrapped around your finger, measure again — the strip should read close to 2.14 in.