Measure your finger circumference and see the corresponding ring size in BR (aro), ISO, US and UK — based on NBR 16058.
The Brazilian ring size — the "aro" — is defined by ABNT NBR 16058:2012, which is based on ISO 8653. The defining measurement is the internal circumference of the ring in millimetres, and the aro number is simply that circumference minus 40: aro 14 means a ring with an internal circumference of 54 mm, which gives an internal diameter of about 17.19 mm (54 divided by π). The tolerance is ±0.05 mm, which is tighter than most home measurements can achieve — a paper strip gets you close, but a jeweller's mandrel gets you right.
The US scale has no official standard. The Bureau of Standards noted in 1921 that "all attempts to find any printed statement as to what the dimensions of the various sizes are supposed to be, have been unsuccessful", and nothing has changed since: it is a trade convention where size 0 starts at a diameter of about 11.63 mm and each size adds 0.8128 mm. The UK scale was standardised in BS 6820 but is now withdrawn; it uses letters from A to Z and beyond, with a step of 1.25 mm of circumference per letter. Both the US and UK columns on this page are best-fit approximations — jewellers disagree by up to half a size, especially above size L.
One millimetre of circumference is one full aro, and fingers change size with the temperature, the time of day, salt intake and exercise. An evening measurement runs a full aro larger than a morning one, and a wide band needs more room than a thin one. This page gives you a starting point from a paper strip; the final sizing belongs on the jeweller's mandrel. Everything runs in your browser and nothing you type is stored.
Aro (BR) = circumference (mm) − 40. ISO = circumference (mm). Diameter = circumference / π. US (approximate) = (diameter − 11.63) / 0.8128. UK letter: n = (circumference − 37.5) / 1.25, letter = A + n.
The Brazilian ring size, defined by NBR 16058. It equals the internal circumference of the ring in millimetres minus 40. Aro 14 means a circumference of 54 mm.
Yes. Brazil, Italy, Spain and Switzerland all use the same scale: the internal circumference minus 40. The ISO number is the circumference itself, so ISO = aro + 40.
Because the US has no official ring size standard — it is a trade convention, and jewellers disagree by up to half a size. The values here follow the dominant convention (diameter = 0.8128 × size + 11.63 mm), rounded to the nearest half size.
The circumference — it is what the standard defines and it is easier to measure with a strip of paper. The diameter is derived (circumference ÷ π) and harder to measure accurately on a finger.
Good enough to narrow it to one or two aros. For a ring you are buying — especially an engagement ring or a wedding band — have the finger sized on a jeweller's mandrel: it accounts for the knuckle, the band width and the metal.
No. The converter runs entirely in JavaScript on your device. Nothing is uploaded, stored or logged.
Vai.la turns any URL into a short link with click statistics, QR Code and your own biolink.
Vai.la is not responsible for how the tools are used or for decisions made based on their results.