Wrap a paper strip around your finger base, mark where it meets, measure that length. Full guide →
Nearby sizes — tap to preview:
Enter your finger circumference or ring diameter. This ring size calculator returns your size in every major system instantly.
Wrap a paper strip around your finger base, mark where it meets, measure that length. Full guide →
Nearby sizes — tap to preview:
Results match the official ring size chart on this site · Based on ISO 8653 standards
This ring size calculator is built for speed, accuracy, and consistency across all major sizing systems. Here is what sets it apart from most online options.
Output appears the moment you hit Calculate — no page reload, no waiting.
Switch between Circumference and Inner Diameter with one tap. Both give the same accurate output.
Works in all three units. Select your unit before entering — no manual conversion needed.
All four major international sizing systems displayed simultaneously in every result.
Every result matches the official ring size chart exactly — same data, zero inconsistencies.
Large inputs, bold results, no horizontal scroll. Built for one-thumb use on any phone.
Your best match is highlighted. Up to 4 nearby sizes shown as tappable chips for when you're between sizes.
ARIA labels, keyboard navigation, and live region announcements for screen reader users.
100% free. No sign-up, no cookies, no ads. Open the page and use it immediately.
Most sizing tools online produce slightly different results for the same input. Here is why this ring size calculator doesn't have that problem.
This calculator and the ring size circumference chart on the homepage use the identical data array. There is no separate lookup table that could drift out of sync. If the chart shows US 7 = 54.4 mm circumference, entering 54.4 mm here will always return US 7 — guaranteed.
All unit conversions (cm → mm, inches → mm) happen in one step before the lookup, eliminating compounding rounding errors. Results are accurate to within 0.1 mm regardless of which unit you enter in.
US, UK, EU/DK, and JP sizes are all derived from the same circumference value in the same lookup — they're never calculated independently. This prevents the common mismatch where a tool shows US 7 but a corresponding EU size that doesn't actually match.
Several popular tools still use pre-ISO conversion tables from the early 2000s. This calculator's dataset follows current ISO 8653 conventions and is reviewed alongside the main CM chart when the site is updated.
If your ring size calculator result looks off, one of these is almost always the cause.
The single most common mistake. If your ruler shows centimetres and the dropdown says mm, the result will be several sizes too small. Always confirm the unit dropdown matches your ruler before pressing Calculate.
In Diameter mode, measure across the inside opening of the ring — not the full outer width including the band. Measuring outer diameter returns a value 2–4 sizes too large.
Some keyboard locales use a comma as the decimal separator (54,4 instead of 54.4). This calculator expects a period. If your input is rejected, switch to a period and try again.
These are entirely different numbers. A US size 7 ring has a circumference of 54.4 mm but a diameter of only 17.3 mm. Entering 17.3 mm into Circumference mode returns US 3 — completely wrong. Always match the tab to the type of measurement you took.
If your measurement falls nearly halfway between two standard sizes, the calculator picks the closer one and lists the other as an alternative chip below. This is not an error — you are genuinely between standard sizes. Try both; if buying online, size up.
Some mobile browsers auto-zoom into number inputs and change decimal entry behaviour. If you notice unexpected input handling, try your device's default browser at standard zoom (100%) to confirm the result.
Different tools use different source tables — neither is necessarily wrong. This calculator uses the same values as the ring size circumference chart on this site (ISO 8653). For international purchases, always verify against the seller's own size chart before ordering.
The same person's fingers vary in size more than most people expect. Using the tool for the wrong finger — or the wrong hand — is one of the most avoidable sizing mistakes.
Your dominant hand (the one you write with) is typically half a US size larger than the other. If you measured your left hand but plan to wear the ring on your right, re-measure or size up by 0.5.
Most people's ring finger and middle finger differ by at least one US size. Always calculate for the specific finger that will wear the ring — don't guess based on a different finger.
If your knuckle is noticeably wider than the base of your finger, size to the knuckle so the ring can pass over it. A ring guard or sizing beads added by a jeweller can prevent it from spinning once on.
Fingers shrink in the cold and swell in heat. For the most accurate ring size calculator input, measure at room temperature in the late afternoon — fingers are at their average largest at this time.
This calculator returns the most accurate standard size for your measurement — but band width can change which size actually feels right on your finger. Here's what to keep in mind after you get your result.
Thin bands like solitaire engagement rings, stackable rings, and eternity bands up to 3 mm sit close to the skin and size true. The number this calculator returns is reliable without adjustment.
Standard wedding bands and classic signet rings fall in this range. Many people find that a medium-width band feels noticeably snugger than a thin ring at the same calculator size. If you're between sizes, choose the larger one.
Wide bands, chunky statement rings, and most men's wedding bands cover more surface area and compress the skin underneath. A ring this wide at your exact calculator size will feel tighter than expected. Size up at least half a US size.
Comfort-fit rings have a rounded inner surface rather than a flat one. This reduces pressure but the effective inner diameter is slightly smaller. If a jeweller specifies "comfort fit," consider staying at your calculated size or going up half a size if you're near a boundary.
Different ring styles have specific sizing considerations beyond what any ring size calculator can determine alone. Use your result above as the baseline, then apply these adjustments.
Most proposals use a placeholder or estimated size. Order a half size larger than calculated — the ring can be sized down after the proposal, and resizing down is cleaner than up. Many jewellers include one free resize.
If the band will be worn alongside an engagement ring, account for the extra space the engagement ring occupies. Some people find they need half a size larger on the wedding band to keep both rings comfortable together.
Full eternity rings (stones all the way around) often cannot be resized without removing stones. Get your measurement from this calculator, then visit a jeweller to confirm before buying — there is no margin for guessing.
Smart rings like the Oura Ring require precise sizing for accurate health monitoring — even 1 mm off can affect sensor readings. Use this calculator's result, then use the sizing kit provided by the manufacturer before committing to a size.
These materials cannot be resized at all — they must be replaced if the size is wrong. Use this calculator carefully, measure twice, and consider ordering a half size up as a safety margin. Always verify with a physical ring sizer first.
Fashion rings worn on the pinky or index finger often use completely different sizes from your ring finger. Re-run this calculator with a fresh measurement of the actual finger, rather than assuming your ring finger size applies.
Not sure where to start? These are the most commonly ordered ring sizes worldwide — useful as a sanity check after running the ring size calculator, or as a fallback when you genuinely cannot measure.
US 6 – 7 · EU 51 – 54 · UK L – N
Circumference: 51.9 – 54.4 mm (5.19 – 5.44 cm)
Inner diameter: 16.5 – 17.3 mm
US 9 – 10 · EU 59 – 62 · UK R – T
Circumference: 59.5 – 62.1 mm (5.95 – 6.21 cm)
Inner diameter: 18.9 – 19.7 mm
Each quarter-size step in the US system adds approximately 1.25 mm to the inner circumference and 0.4 mm to the inner diameter. Half a US size = ~2.5 mm circumference difference — meaningful enough to feel on your finger.
EU 54 means exactly 54 mm inner circumference. This makes EU sizing the most transparent system — once you have a measurement from this ring size calculator, your EU size is that number rounded to the nearest whole integer.
Weight changes, pregnancy, arthritis, and aging all affect finger size. A ring measured perfectly at 25 may feel tight at 45. If buying a permanent ring in a non-resizable material, consider this when choosing a size.
For the full ring size circumference chart with every value in mm, cm, and inches across all systems, visit the main ring size chart or check the chart in cm.
The complete reference chart — US, UK, EU/DK, JP sizes with circumference and diameter in mm and inches. The same values this calculator uses.
All standard ring sizes with circumference and diameter expressed in centimetres — useful if your ruler only shows cm markings.