About
About us
ringsizeai.com is a free ring size calculator, chart and printable sizer. It exists because most online ring sizers draw a circle at a fixed pixel size and call it a millimetre — which it is not, on any two devices alike. Ours calibrates your screen first.
How we work
Four rules the whole site is built on
- 01
Calibrate before measuring
Screens differ in pixel density, so a circle drawn at a fixed pixel size is a different physical size on every device. The sizer asks you to match a bank card or a ruler first, then draws every circle from that scale. Without that step the number is decoration.
- 02
One standard, stated plainly
Inside circumference in millimetres is the base unit, following ISO 8653. US, UK, EU, Indian and Japanese sizes are all converted from it, so the same finger gives consistent answers across every chart on the site.
- 03
Nothing leaves your device
Measuring runs entirely in the browser. Your calibration and your size are stored locally, never uploaded, and never tied to an account — there is no account.
- 04
Say where the limits are
A screen sizer is accurate to roughly a fifth of a US size when calibrated against a card, and to about half a size when it is not. Every one of those figures is published as an error budget rather than asserted. For a permanent purchase, a jeweller with a steel mandrel is still the final word, and we say so rather than overselling the tool.
Where the numbers come from
Every size on the site is derived from a single table of inside circumferences in millimetres. US sizes follow the standard 0.8128 mm per half-size progression from a size 0 at 37.8 mm circumference; UK letters, EU/ISO numbers, Indian and Japanese sizes are mapped onto the same millimetre values. Because one table feeds theinternational chart, theUS chart, themen's chartand the sizer itself, the conversions cannot drift apart.
Accuracy claims are treated the same way: theaccuracy and methodology pagederives the ±0.15 mm, ±0.3 mm and ±0.5 mm figures line by line rather than asserting them.
Guidance pages — such ashow to measure at home— are reviewed and dated. The review date appears in the page metadata so you can tell how current a page is. If you find something wrong, tell us and we will correct it.
The site carries no accounts, no sign-up and no measurement upload. What that means in detail is set out in theprivacy policy, and the terms of use are in theterms & conditions.