How the measurement works

Three inputs, three meanings

Finger mode

Matches two guides to visible finger width. That width is treated as an equivalent circular diameter for a rough size lookup. Finger circumference has not been measured.

Ring mode

Matches a circle to the inner opening of an existing round ring. The selected diameter depends on screen scale and the user’s alignment.

Number converter

Converts an entered size, inner diameter or circumference. It performs no physical measurement and does not decide whether a ring will fit.

For circular geometry, circumference = π × diameter. Applying that relationship to a visible finger width does not prove that the finger has that circumference. This is why finger results are labelled estimates.

How does the website set the screen scale?

A CSS pixel is a layout unit, not a fixed physical millimetre on every screen. The browser’s device pixel ratio alone does not tell us a panel’s physical pixel density.

Android model matching

On a supported Android mobile browser, the page asks User-Agent Client Hints for its model field. A known exact model can match a local screen profile. If the browser does not return one within 1.2 seconds, the page tries an exact model in an older user-agent string. A generic model such as “K” is not enough. Chrome’s documentation explains that the browser controls which values it supplies.

For Pixel profiles, panel width in mm = native pixel width ÷ published PPI × 25.4. For the Samsung profiles, width comes from the published full-rectangle diagonal and pixel aspect ratio. Current full-screen CSS width ÷ panel width in mm gives CSS pixels per millimetre. This avoids assuming that Android’s rendering resolution or logical density is its physical PPI.

iPhone screen matching

The current iPhone presets use published PPI and an expected normal-display rendering ratio. The browser information used here does not uniquely identify the exact model. We match the screen configuration only when the matching candidate presets share the same scale, and label the result screen-match estimate. Another device with identical reported parameters can still be indistinguishable.

Configuration checks and fallback

The tool checks portrait orientation, screen dimensions, viewport width, device pixel ratio and available visual viewport scale. A screen or zoom change invalidates the previous setup and confirmed result. These checks can catch configuration mismatches; they do not validate the actual physical scale.

Unknown or mismatched screens can use an explicit preview, which cannot be exported as a measurement. Optional ruler setup compares an on-screen line with 20 mm on a physical ruler. The website requests no camera access.

Which phones have screen profiles?

There are 14 profiles below. They are based on published specifications and are all awaiting physical validation. Android auto-detection needs a recognised model identifier; Pro, Plus, Ultra, XL, a and folding variants are not interchangeable.

A profile being listed does not guarantee browser identification, exact screen matching or measurement accuracy. Normal display settings and a full-width portrait browser remain part of setup.

Where do the international sizes come from?

The GIA international table supplies US 3–13.5 half-size diameters and the UK and Japanese mappings used here. Peter Stone supplies extended US 14–15 diameters. We preserve missing UK and Japanese entries instead of filling them by interpolation.

EU values here are approximate inner circumference, calculated as π × the reference diameter and rounded to a whole millimetre. Other charts may place a US size at another letter or fraction. We do not claim ISO certification or that every jeweler uses this table.

Measurement inputs select the nearest listed inner diameter in the range 14.1–23.8 mm. Inputs outside the range do not produce a substituted boundary size. Adjacent finger-result sizes are nearby table rows to compare, not a confidence interval.

What has been checked, and what remains unknown?

Automated checks cover reference data, scale calculations, converter inputs, configuration rejection, browser interaction and exported files. Mobile browser simulations check layout and logic. PDF geometry can be inspected digitally. None of these checks establishes physical measurement accuracy.

Not yet completed: ruler-to-screen checks across real phones and display settings; physical printer checks; controlled comparisons of visible finger widths with finger gauges and real ring fit. There is no demonstrated ±0.2 mm tolerance or percentage accuracy for this tool.

Finger shape, pressure, alignment, knuckle clearance and band design affect fit. The tool does not add fixed temperature, knuckle or band-width corrections. Use a physical fitting and the retailer’s chart for the ring you plan to buy.

What happens to my phone information and measurements?

The tool code matches model information and calculates measurements in your browser. It does not send phone models or readings to an identification or measurement service. No camera, account or payment is needed.

A manually confirmed supported phone choice may be saved in localStorage with its screen configuration; an optional ruler scale is kept in sessionStorage. Confirmed sizing results are not automatically restored. You can remove this local state by clearing this site’s browser data.

A shared return link or QR code contains the selected method and reading in its URL. Share it only when you want to share that reading. The hosting service receives ordinary web requests and may process request logs; anonymous Umami statistics count page visits and fixed tool steps, without measurement readings or selected phone profiles. It honours DNT/GPC and does not set analytics cookies. See the privacy policy for retention and deletion details.

Use the measurement guide to choose a method, or return to the phone estimator with these limits in mind.