Measure Your Ring Size
in 60 Seconds

PerfectRingSize is a free online ring size measure tool that turns any phone, tablet or laptop into an accurate ring sizer. There is nothing to download, nothing to print and no ruler required. Two measuring methods cover both situations people actually find themselves in — measuring a ring you already own, and measuring a bare finger — and each returns your size in US, UK, European and Indian standards at the same time, so you can order confidently from a jeweller anywhere in the world.

How the ring size calculator works

Both methods rest on the same idea: a standard credit card. Every payment card in the world is manufactured to the ISO/IEC 7810 ID-1 standard, measuring exactly 85.60 mm by 53.98 mm, which makes it a precise physical ruler that almost everyone already carries. The Screen Sizer asks you to resize an on-screen rectangle until it matches your card, establishing exactly how many pixels your display renders per millimetre; you then resize a circle to match the inner edge of your ring. The Camera Sizer applies the same reference alongside MediaPipe hand-landmark detection to measure the width of your ring finger's largest knuckle in real time.

Which method should you use?

If you already own a ring that fits the finger you are buying for, use the Screen Sizer. Measuring a solid object is inherently more reliable than measuring a soft, changeable finger, and it remains the most accurate way to measure ring size at home. If you have no reference ring, the Camera Sizer measures your finger directly and lands within about half a millimetre — comfortably inside the half-size tolerance most ring manufacturers work to. If you would rather work on paper, the printable ring size chart covers the same ground. There is a fuller walkthrough of the options in how to measure ring size without a ring.

Getting an accurate result

Ring size is not a fixed number. Fingers swell and shrink through the day, and the gap between a morning and an evening measurement is often a full half size. Measure in the evening, when your hands are warm and at their largest, and avoid measuring straight after exercise or in a cold room. Take the reading two or three times and use the largest. Two other factors matter just as much: knuckle size and band width. If your knuckle is wider than the base of your finger, the ring has to clear the knuckle before it can rest, so size up. Any band wider than 6 mm sits higher on the finger and fits tighter — add half a size, or a full size beyond 8 mm.

Your privacy is protected

Everything happens inside your browser. The camera method runs its AI model locally on your own device, so no photos, video frames or biometric data are ever uploaded to a server. Your measured size is stored only in your browser's local storage, and you can clear it at any time from the badge in the corner of the screen. There is no account system and nothing to sign up for.

Ring size charts and conversions

Once you have a measurement in millimetres, converting it is straightforward. The chart above covers whole sizes, while the full ring size chart lists every size from US 2 to 13 with both inner diameter and circumference, mapped across US, UK, EU and Indian standards. There are dedicated references for the men's ring size chart and the average ring size for women, every individual size has its own page with exact measurements and fitting notes, and the ring size guide answers the questions that come up most — including what to do when you fall between two sizes and whether a ring size adjuster is worth using.