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Measure Ring Size Online — Free Ring Sizer & Calculator
Find your ring size with easy online measurement tools. Measure an existing ring, use your finger circumference, or convert measurements into international ring sizes.
Choose how you want to measure
Prefer a focused page? Online Ring Sizer · Calculator
Try the tool
The tool below follows the choice you made above. You can also switch methods inside it — the selector at the top of the tool stays in the same place, so the page does not jump.
Step 1 — Calibrate with a bank card
Step 1 of 2
Place a real bank card flat against the screen. Adjust the rectangle below until its edges line up with the card. The rectangle's height follows the card's proportions automatically, so matching the width also checks the height.
If the rectangle is wider than your screen, rotate to landscape or use a larger screen — do not guess the card's width.
No size is shown until you confirm calibration. Skipping calibration would produce a fabricated result, so the tool refuses to guess.
Step 2 — Match the circle to the ring's inner edge
Step 2 of 2
Diameter and circumference appear here once calibration is confirmed.
Enter a diameter in millimetres, then Apply. It must be inside the chart range (12–24 mm).
How it works
Three steps, under a minute once you have a card and a ring — or a paper strip and a ruler.
Calibrate
Match the rectangle to a standard bank card (85.6 mm wide) so the tool learns your screen's pixels per millimetre.
Measure
Match the circle to the inside edge of a ring that fits, or type a diameter or circumference.
Convert
Read your US, UK (approx.) and EU size, plus diameter and circumference — and size up if you are between sizes.
International ring size chart
A short extract from the full reference table. UK letters are approximate — see the chart page for the full table and notes.
Scroll sideways to see all columns.
| US / Canada | UK (approx.) | Australia (approx.) | EU / ISO | India (approx.) | Inner diameter | Inner circumference |
|---|---|---|---|---|---|---|
| 5 | J | J | 49 | 9 | 15.70 mm | 49.3 mm |
| 6 | L | L | 52 | 12 | 16.51 mm | 51.9 mm |
| 7 | N | N | 54 | 14 | 17.32 mm | 54.4 mm |
| 8 | P | P | 57 | 17 | 18.14 mm | 57.0 mm |
| 9 | R | R | 60 | 20 | 18.95 mm | 59.5 mm |
| 10 | T | T | 62 | 22 | 19.76 mm | 62.1 mm |
Measurement methods
Three ways in, one chart out. Pick the method that matches what you already have.
An existing ring
The most reliable at-home method. You are copying a known fit, not estimating a finger. What is measured is the ring's inner diameter, matched on screen after card calibration.
Finger circumference
Best when there is no ring to copy. A paper strip wrapped around the finger gives a circumference, which the calculator converts. It depends more on how snugly and when you measure, so repeat it and take the largest reading.
Numerical conversion
Best when you already have a number — from a jeweller, another chart, or a ruler. Type a diameter or circumference in millimetres, centimetres or inches and convert it to US, UK (approx.) and EU sizes without re-measuring.
Accuracy and calibration
Home measurement is useful and honest about its limits. These three points decide whether a result can be trusted.
Screen calibration matters
Every screen shows a different number of pixels per millimetre, so the sizer cannot know a size until it is calibrated. A standard bank card (85.6 mm wide) is the reference: match the rectangle to a real card, held flat against the screen, and the tool learns your device. A tilted card, or no calibration at all, would produce a fabricated result — which is why the tool shows no size until calibration is confirmed.
Home measurements are approximate
Done correctly, at-home results typically land within half a US size of a professional measurement. Fingers change size through the day, with temperature and with band width, so a home result is a strong guide for ordering — not a guarantee of fit. Measure in the evening, repeat twice, and size up if you are between sizes.
Why you can trust this result
- Calibration uses a standard bank card (85.6 mm wide, ISO/IEC 7810 ID-1) — a physical reference, not a guess about your screen.
- Your measurement is calculated in your browser and is not sent to a server. There is no account, and analytics runs only if you consent to it.
- Results are guidance, not a guarantee. For an expensive or hard-to-resize ring, confirm with a professional fitting.
Related guides
- How to measure ring size
Which method to use, starting from what you already have — a ring, a finger, or a number.
- How to measure ring size at home
Paper strip, existing ring, and screen sizer — step by step, with the mistakes to avoid.
- International ring size chart
The full US 3–13.5 table with diameter, circumference, UK (approx.) and EU sizes.
- Measurement methodology
Formulae, calibration, tolerance, and what this tool does not claim.
Frequently asked questions
With correct card calibration and a ring that already fits, most people land within half a US size of a jeweller measurement. Measure in the evening, when hands are warm, and repeat two or three times, taking the largest reading.