Free Online Ring Sizer
Free, no sign-up, and phone friendly. Measure with a ring, paper strip, known measurement, or optional AI photo—four methods in one tool.
Lay a bank card flat on the screen, then adjust the outline until it matches the card exactly.
Keep the card flat, not tilted. Calibration is saved on this device.
How calibrated measurement works
Bank-card calibration — an object with a standard ISO size, not a rough on-screen image.
Quarter US sizes, converted to UK, EU and JP in real time.
Manual methods stay on your device. The optional AI photo is sent temporarily to the vision service and is not stored by Belaroq.
Common sizes at a glance
A short reference for common whole US sizes. Open the dedicated chart for all 41 quarter-size conversions.
| US / CA | UK / AU | EU / ISO | Asia / JP | Ø mm | mm |
|---|---|---|---|---|---|
| 4 | H | 47 | 7 | 14.9 | 46.8 |
| 5 | J | 49 | 9 | 15.7 | 49.3 |
| 6 | L | 52 | 11 | 16.5 | 51.8 |
| 7 | N | 54 | 14 | 17.3 | 54.3 |
| 8 | P | 57 | 16 | 18.1 | 56.9 |
| 9 | R | 60 | 18 | 19 | 59.7 |
| 10 | T | 62 | 20 | 19.8 | 62.2 |
Our team can confirm the production size. Resizing and returns depend on the design and the conditions in the published policy.
Planning a custom lab-grown diamond ring? Record your US size, measured millimeters and intended band width with your design. Check the resizing conditions before confirming production.
Accuracy & methodology
Physical dimensions and regional mappings follow GIA's international chart. EU/ISO is the rounded inner circumference in millimeters under ISO 8653. If a regional equivalent is not published, the tool shows — instead of guessing. Calibration sets pixels per millimeter from the displayed card width divided by 85.6. A measured ring diameter is the inner-circle pixel width divided by that scale; circumference is diameter × π. Recalibrate after changing device, zoom or screen orientation. Repeat three times and cross-check with a second method. Quarter-size steps describe the controls, not guaranteed measurement accuracy; paper tension, ring alignment and knuckle fit can change the result.
How to use the Belaroq Ring Sizer
A 50-second visual walkthrough of calibration, ring matching, the paper-strip method, and a second-method check.
Transcript
First calibrate the screen with a bank card. For an existing ring, match its inner edge to the circle. Without a ring, mark a paper strip and measure it against the calibrated ruler. Save the result, then confirm it with a second method.
Ring-sizing method: calibration and repeatability
Reviewed by Belaroq Jewelry & Product Team · · Method version 1
A description of the Belaroq tool and printable method, with worked calculations. Examples are not physical accuracy tests or a guarantee of fit.
How the screen scale is calculated
Screen pixels per millimeter = matched card edge in CSS pixels / reference card edge in millimeters. Ring inner diameter = circle width in CSS pixels / screen pixels per millimeter.
Worked screen example: a matched 85.6 mm card edge spanning 428 CSS pixels gives 5 pixels per millimeter. A circle 86.5 pixels wide represents a 17.3 mm inner diameter; the nearest shared chart row is US 7, UK N, EU 54.
- Use a standard bank card matching the reference dimensions; align the full edge flat against the screen.
- Calibrate on the same screen, browser zoom and orientation used for the measurement. Recalibrate after any change.
- For ring matching, align the circle to the inside edge of a ring that fits the intended finger, not the outer metal edge.
- A paper-strip measurement should sit comfortably and pass over the knuckle; stretching or pulling changes the result.
Repeat and record the measurement
- Record three separate measurements for the same finger and hand, removing and repositioning the ring or strip between readings.
- Record the method, raw millimeters, browser zoom or print setting, and the lowest and highest readings.
- Cross-check against an independent method or a professional fitting, especially when readings map to different sizes.
- Confirm the intended band width, knuckle passage and comfortable fit with Belaroq before production; do not average away conflicting readings.
The tool selects the nearest supported row of the shared ring-size chart. EU is rounded inner circumference in millimeters. Numerical step size and quarter-size labels are not a measurement-accuracy claim.
A 1 mm error in measured inner diameter changes the calculated circular circumference by about 3.14 mm. This geometric relationship is not a tolerance or a measured error range for the tool.
Suggested citation: Belaroq. Ring-sizing method: calibration and repeatability. Method version 1, reviewed 2026-09-30. Canonical method and worked example.
Reference sources: GIA: Ring size guide and chart; NIST: The inch is exactly 25.4 millimeters. The reference sources do not certify or validate the Belaroq tool.
Ring sizer questions, answered
Is the Belaroq online ring sizer free?
Yes. Belaroq's online ring sizer is free and requires no sign-up. Use a calibrated screen to match an existing ring, measure a paper strip, or enter a known inner diameter or circumference. Results use the shared US, UK, EU and JP ring-size chart.
How can I measure my ring size at home?
With a ring that fits the intended finger, calibrate the screen with a bank card and match the ring's inner edge to the circle. Without a ring, mark a paper strip around the finger and measure its length with the calibrated ruler. Repeat three times and cross-check with a second method before choosing a production size.
Is the online ring sizer accurate?
Bank-card calibration converts screen pixels to millimeters using the card's 85.6 × 53.98 mm reference dimensions. Accuracy depends on calibration, alignment and finger fit; quarter-size controls do not guarantee quarter-size measurement accuracy. Repeat the measurement and confirm non-resizable pieces with Belaroq before production.
Why calibrate the screen with a bank card?
Every screen renders pixels at a different scale. A bank card has a standardized size, which lets us convert pixels into real millimeters on your device.
How do I measure without an existing ring?
Use the paper strip method: wrap a narrow strip around the base of your finger, mark the overlap, flatten it, and compare it against the calibrated on-screen ruler.
When should I measure my finger?
In the evening at room temperature. Avoid mornings, right after exercise, after salty meals, or in cold weather, because finger size shifts through the day.
What if I am between two sizes?
Choose the larger size for comfort, especially for wide bands (6 mm and up), which feel tighter. Belaroq confirms the production size on request.
What if the delivered size does not fit?
Contact Belaroq before returning the ring. Resizing eligibility depends on the design, and returns remain subject to the exclusions and conditions in the published 60-day policy.
Is my measurement private?
Manual calibration and measurement stay in your browser. If you choose the optional AI photo method, the image is sent temporarily to the vision service for analysis and is not stored by Belaroq.
Does the ring sizer work on a phone?
Yes. Open this page in your phone's browser, calibrate with a bank card, then place your ring or paper strip directly on the screen.