About
Online Ring Size is a free tool for measuring your ring size on screen and converting it into every country’s sizing standard. It exists because almost every other on-screen sizer stops at a bare number, and a bare number is the one thing a ring size shouldn’t be.
A ring that is half a size out still doesn’t fit. It spins, or it won’t clear a knuckle, and either way it goes back. The gap between a good sizer and a bad one is not the circle drawn on the screen — that part is trivial. It’s everything around it: whether the screen is calibrated at all, whether the calibration can be checked, whether band width and knuckles are accounted for, and whether the tool is honest about the error left over at the end.
We started by measuring the competition rather than the fingers. Most tools drew a circle at an arbitrary scale and hoped. Several asked for a credit card and offered no alternative. One shipped a conversion chart with a size listed twice. None of them printed a tolerance. So this was built the other way round: start from the published standards, make calibration verifiable, and put the error bar on the screen next to the answer.
Each of the 11 national standards is implemented as the formula its own standards body published — ISO 8653 for the European circumference scale, JIS S 4700 for Japan, NBR 16058 for Brazil, the 0.8128 mm-per-size US trade scale, the Wheatsheaf letter scale for Britain. Nothing is a hand-keyed lookup table. Typed tables drift and pick up errors; we found a duplicated size in a competitor's chart while researching ours.
Every result carries a stated accuracy range, and we tell you which step is limiting it. Calibration error is proportional and measurement error is absolute, so we combine them in quadrature — the standard way of adding independent uncertainties. That range is the most useful thing on the results screen, and most sizers don't show it at all.
Most on-screen sizers assume a credit card. Card ownership is not universal, and a tool that assumes it isn't really global. You can calibrate against a coin from your own currency, a folded sheet of A4 or Letter, a ruler, or your device's published pixel density — then verify the scale with a second object.
The whole calculation runs in your browser. There is no account and no upload — no measurement, calibration value or result is ever sent to us. Your calibration is saved in your own device's local storage so you don't have to redo it, and clearing your browser data removes it. We count page views with Google Analytics, and the site carries advertising; both see that a page was opened and nothing about what you measured on it.
At a typical screen density, one pixel of misalignment is already about a fifth of a US size. That is a physical floor no amount of arithmetic gets past. For a ring you cannot return, we say plainly: get sized on a steel mandrel at a jeweller. Use this to know what to expect before you walk in.
The business model
It’s a fair question, and the honest answer starts with how little the site costs to run. It’s a set of static files with no database and no servers doing work per visit, and the calculation happens on your device rather than ours. Hosting a few hundred pre-built HTML pages is close to free.
The rest comes from advertising, and in time from a commission if you buy through a link here. Neither is live yet. When they are, the ads will sit in their own marked slots, sold by Google rather than chosen by us, and any affiliate link will be labelled where it appears. There is also a paid version of the sizer for jewellery stores — which is what we would rather this ran on eventually, because it asks nothing of you at all.
What none of that touches is the measuring. Your calibration and your size are worked out in your browser and never sent anywhere, so there is nothing about your hands for an advertiser to receive. And every size here is computed from published national standards: no commission moves a chart, a recommendation, or one of the confidence ranges. If a retailer asked us to change a number, the answer would be no.
You can hold us to that. The privacy policy was updated before the first ad rather than after it — sections 4 and 5 set out exactly what each one collects, what it cannot see, and how to switch it off.