Calculadora de Tamanho de Anel
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
diâmetro = circunferência / π; BR = diâmetro_mm; US = (diâmetro − 14.86) / 0.832 + 1
About this calculator
The Ring Size Calculator is a practical tool to convert your finger circumference into Brazilian ring numbers and US sizes. Simply measure the finger perimeter in millimeters, and the calculator uses straightforward formulas to determine the equivalent diameter and then the corresponding sizes. The result is displayed instantly, making it easy to choose the perfect ring for yourself or as a gift.
How it works: first, the diameter is calculated by dividing the circumference by π (approximately 3.1416). In the Brazilian system, the ring number directly matches the diameter in millimeters. For US sizes, the formula is: US = (diameter - 14.86) / 0.832 + 1. The result is rounded to the nearest half size, following US commercial standards.
When to use: this calculator is ideal for buying rings online, confirming your size before ordering custom jewelry, or converting between Brazilian and US sizing systems. It is also useful for retailers serving clients with international references.
Precautions: measure your finger circumference with a flexible tape measure or string at the end of the day (when fingers are slightly swollen) and at room temperature. Avoid measuring after physical activity or on very hot days. For best accuracy, take three measurements and use the average. Remember that wide rings may require a slightly larger size.
Frequently asked questions
How to measure finger circumference correctly?
Use a flexible tape measure or a string. Wrap it around the base of your finger without squeezing, and mark where the end meets. Measure the length with a ruler. Do this at the end of the day when fingers are slightly swollen.
Is Brazilian size the same as diameter in mm?
Yes, in the Brazilian system, the ring number directly matches the inner diameter in millimeters. For example, an 18 mm diameter equals size 18.
What is the difference between Brazilian and US sizes?
Brazilian size is based on diameter in mm, while US size uses a numerical scale with half sizes. The calculator automatically converts between the two systems.
Can I use this calculator for wide rings?
Yes, but for rings wider than 6 mm, it is recommended to choose a half size larger than the calculated one, as the fit may feel tighter.
What if my finger is between two sizes?
Choose the larger size if the ring is for fingers that swell often. For engagement rings or wedding bands, prefer a comfortable fit that is neither too tight nor too loose.