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Ring Sizer

Ring size in Mexico vs the US: how do you convert?

Ring Sizer has no Mexico option in either picker, so the reliable route is millimetres: get the circumference or inside diameter, then read the US number off the System Converter. A 57 mm circumference comes out as US 8 (UK Q, EU 17, JP 16).

2 min read · Updated 2026-09-10

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There is no Mexico column in the app, despite many search results implying one exists. The System Converter card has six systems in its From and To menus: US (American), JP (Asian), EU (Swiss), Circumference (mm), Diameter (mm) and UK / AU. Six, and Mexico is not one of them.

There is no single Mexican scale that every jeweller follows, so none is assumed here. Some shops list US-style numbers, some a local number, some only millimetres. The millimetre is the one thing they all share, so that is the common unit to convert through.

Convert a Mexican listing through millimetres

  1. Find the circumference or inside diameter on the seller's size chart, in mm. Many charts have a column for it.
  2. Open System Converter and set From to Circumference (mm) (or Diameter (mm)).
  3. Type the number in the size field. The slider below it works too.
  4. Set To to US (American).
  5. Leave Fit Type on Standard (no adjustment) unless the band is wide.
  6. Read UK, EU and JP in the All Equivalents list. Copy Result copies only the one converted size, so for the seller's message type out the millimetres yourself.

A chart that says only 'talla 8' with no millimetres is a dead end — the scale cannot be guessed. Ask the seller for the inside diameter.

Worked example: a 57 mm ring

Circumference 57 mm entered in System Converter (All Equivalents list)
SystemResult
US8.00
UKQ
EU17.00
JP16.0
Diameter18.14 mm

All five values come from one row of the app's table, so they agree with each other. One quirk: the circle screen in Ring Sizer shows 56.9 mm for that same 18.1 mm diameter, because it multiplies by pi, while the converter shows 57.00 from the table — a 0.1 mm gap that can safely be ignored.

When you have no number at all

Then measure. Calibrate once under Calibration, then use Ring Sizer with a ring you own or Finger Sizer without one. US, UK, EU and JP sizes update as you move the slider, and you can type the mm figure into the converter if a seller wants another system.

Cost: none. System Converter, the full chart and the sizer screens are free, with a banner ad that Premium removes.

Questions and answers

Are ring sizes different in Mexico?
It depends on the seller. Some list US numbers, others use their own numbering or only millimetres. The app has no Mexico setting, so converting through the circumference or diameter in mm is the reliable approach.
How do I convert a ring size from Mexico to US?
In System Converter, choose Circumference (mm) or Diameter (mm) as the source and US (American) as the target, then type the millimetre figure from the seller's chart.
What is a size 7 ring in Mexico?
This cannot be answered without knowing the seller's scale. In US numbers, size 7 is a 17.2 mm inside diameter and 54 mm circumference in the app's table.
Does the converter work offline?
Yes. The converting itself needs no connection. Ads and the App Store price do.

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