cm to Ring Size Converter

How to measure your ring size at home

The simplest method is the paper strip technique. Cut a thin strip of paper (or use a length of string), wrap it snugly around the base of your finger, mark where the two ends meet, then measure the length against a ruler in centimetres. That length is your finger circumference. Enter it into this converter and it will look up the closest ring size. Alternatively, if you already own a ring that fits the same finger, measure its inside diameter: lay the ring flat, place a ruler across the inside from edge to edge, and note the distance in centimetres, then choose the "inside diameter" mode. For the most accurate reading, measure later in the day when fingers are at their largest, and at room temperature: fingers shrink in the cold and swell in the heat.

How the converter works

Ring sizing systems differ by country but all trace back to two physical quantities: inside diameter and inside circumference (which are linked by pi). The US/Canada system uses a numeric scale that increases roughly every 0.83 mm of diameter. The UK/Australia system uses letters (A through Z+). France and Russia use a number that approximates the circumference in millimetres. Germany uses the inside diameter in mm divided by a constant offset. Switzerland uses a similar diameter-based scale. Japan follows the JIS standard, also approximately circumference-based. This converter finds the closest entry in a calibrated lookup table drawn from ISO 8653 and jeweller trade standards, then reads off the corresponding size for each system. Because the systems were designed independently, some US or UK sizes have no exact equivalent abroad, shown as a dash in the table.

Tips for an accurate ring size

Finger size fluctuates by as much as half a US size throughout the day, with humidity, temperature, and exercise all playing a role. For the most accurate result: measure at the end of the day when your fingers are slightly larger; measure three times and take the middle value; use a proper metal ring mandrel at a jeweller for fine jewellery. If you are between two sizes, choose the larger one for comfort, but go down half a size for a wide band (over 6 mm), since wider bands grip the finger more and feel tighter. Dominant hands are sometimes half a size larger, so measure the specific finger you plan to wear the ring on.

Which ring size system is used in your country?

US and Canada use the numeric scale common to most online retailers worldwide. The UK, Ireland, Australia, and New Zealand use the alphabetic system (A to Z+1). Most of continental Europe - including France, Russia, Italy, Spain, and the Netherlands - uses the French/Russian numeric system based on circumference in millimetres. Germany and Austria use the German diameter-based scale. Switzerland has its own similar diameter scale. Japan uses the JIS standard, close to the French system. India generally follows UK sizing. If you are ordering from an international retailer or buying abroad, always confirm which standard they use before ordering.