BR Ring Size from Finger Circumference mm

Brazilian ring size from finger circumference (mm)

In Brazil rings are numbered by the "Aro brasileiro" system, and the trick is that the ring number is just its inner diameter in millimetres. A few anchors help: ring 12 has a 16.5 mm inner diameter, ring 16 sits at 18 mm, and ring 20 at 19.5 mm. If you know the finger circumference, divide it by π to get that inner diameter: diameter = circumference / π. Take a 53 mm finger as an example. That works out to a diameter of about 16.87 mm, which lands on Brazilian ring size 14. Measure when your hands are warm, since cold fingers shrink a little, and remember your dominant hand usually runs slightly bigger.

Applications

You will see this in jewellery shops, in online wedding band sizing, and with manufacturers who dimension their metallic rings to ABNT NBR 15660. International stores that offer a size swap across BR / US / UK / EU numbering lean on it too. Every printable ring sizer you can download is built on the same circumference-to-mm chart.

FAQ

BR ring 16 is what in US sizing? It comes out around US 7.5. Still, double-check against the seller's own chart, because US sizing runs in fractional steps.

Should I measure with string or paper strip? Go with a paper strip. String stretches as you pull it, so you end up with a reading that's too big.

What if the ring has a wide band? Wide bands sit tighter on the finger, so go half a size up (BR +0.5 to +1) once the band is wider than 6 mm.