About
Actual Ring Size is a single-purpose tool: work out your ring size on screen, accurately, without an account and without being sold anything.
Why it exists
Most on-screen ring sizers share two faults. They do not notice when the browser zoom changes, so a calibrated circle silently stops being true size. And they do not control printing, so the browser shrinks the page to fit the paper and the printed chart comes out a few percent small — which is a whole ring size. This site fixes both, and that is essentially the whole reason it was built.
Where the numbers come from
Sizes follow ISO 8653:2016, which defines a ring size as the inner circumference in millimeters. US and UK equivalents use the published conversion, with UK letters stepping 1.25 mm per alphabetical step from size C = 40 mm per British Standard BS 6820. Screen calibration uses the ISO/IEC 7810 ID-1 card format, nominally 85.60 × 53.98 mm — the size of every bank and ID card in the world.
Nothing on the chart is estimated. If a figure is not derivable from those standards it is not shown.
How it handles your data
It does not collect any. The tool runs entirely in your browser: no measurement, image or input is uploaded, and there is no account to create. Your screen calibration is stored in your own browser so you do not have to repeat it, and it never leaves your device.
Honest limits
An on-screen measurement is a good guide, not a guarantee. Curved screens, a card held at an angle, or a finger measured only once on a cold morning will all shift the answer. For an engagement ring or anything hard to return, confirm with a jeweler.