About Us
PerfectRingSize is a free tool for measuring ring size accurately in a browser — without printing a chart, downloading an app, or visiting a jeweller.
Why we built this
Buying a ring online is straightforward until you reach the size dropdown. At that point most people are guessing. The usual advice — print this PDF at 100% scale, or wrap a piece of string around your finger — fails quietly: printers silently rescale pages by three to five percent, and string compresses as you pull it. Neither tells you it has gone wrong, and half a size is the difference between a ring that fits and one that does not.
We wanted a method where the calibration is visible and checkable. Holding a credit card against a rectangle on your screen and adjusting until they match is something you can verify with your own eyes in about ten seconds. Everything else follows from that one honest reference measurement.
How we approach it
Private by default
The camera model runs on your device. No photos, video frames or biometric data ever leave your browser, and there is no account to create.
Calibrated, not guessed
Every measurement is anchored to a credit card, which is manufactured to 85.60 mm worldwide under ISO/IEC 7810. That removes screen and camera variation from the result.
No printing, no app
Printed charts are distorted by printer scaling, and an app is a lot to ask for a one-minute task. Both methods run in a normal browser tab.
How the measurements work
The Screen Sizer calibrates against a credit card to establish how many pixels your display renders per millimetre, then measures the inner diameter of a ring you place against the screen. Because it measures a solid object rather than a soft finger, it is the more accurate of the two methods.
The Camera Sizer uses MediaPipe hand-landmark detection to locate the joints of your ring finger and measure the width of the widest knuckle, smoothing the reading across many frames before it settles. It exists for the common case where you have no reference ring at all.
Both produce a measurement in millimetres, which is the only number that actually matters — every national sizing standard is derived from it. Our conversion table covers US and Canada, UK and Australia, EU and Germany, and India, from US size 2 to 13, and is published in full on the ring size chart.
What this tool is not
It is a measuring aid, not a guarantee. Fingers change size through the day and across the seasons, band width changes how a given size feels, and knuckles complicate things further. For an expensive or hard-to-resize ring — an eternity band or a tension setting, neither of which can usually be resized afterwards — confirm your size with a jeweller before ordering. We say the same thing on every result page, because it matters more than any measurement we can give you.
Who runs it
PerfectRingSize is independently run — not a jewellery retailer, and not funded by one. We do not sell rings, take commission on them, or share your measurements with anyone, which means the size we give you is not influenced by what someone wants to sell you. If you have found a bug, disagree with a measurement, or want to tell us the tool got your size wrong, we genuinely want to hear it.