Ring Size Converter

Overview

Ring Size Converter works through inside diameter in millimetres. A lookup table maps US sizes 3 to 14 in half sizes, UK letters F to Z plus Z+1 and Z+2, and EU sizes 44 to 66 to diameters from 14.1 mm to 23.0 mm. The `size` and `from` parameters are converted to a diameter first; the `measurement` parameter, a diameter from 10 to 30 mm, skips that step and takes priority when both are sent.

For `from=us` and `from=eu`, a size missing from the table is interpolated at 0.4 mm per step, so a quarter size still converts. For `uk` and `au`, the letter must be in the table or the call returns a 400. `jp` input is read directly as a diameter. `ch` input is treated as a ring number equal to the inner circumference minus 40.

From the diameter, `circumference_mm` is diameter times pi, rounded to one decimal. `us`, `uk` and `eu` are the table entries whose diameter is nearest, so output US sizes always land on a half size. `au` is the same letter as `uk`. `jp` is the diameter truncated to a whole millimetre. `ch` is the circumference minus 40, truncated to a whole number. `input_diameter_mm` and `conversions.diameter_mm` echo the diameter actually used, which for interpolated or `ch` input can carry more decimals than the table values.

On the Free plan `eu`, `jp`, `ch` and `au` are removed from `conversions`; the diameter, circumference, `us` and `uk` remain.

Live Test Ring Size Converter API →

Endpoint

One host, one path per API. The block below shows this call in four languages; every one of them is the same HTTP request. Making requests covers the timeouts, retries and parameter rules that apply to all of them. The SDKs wrap the same call in a typed client.

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curl "https://api.apiverve.com/v1/ringsizeconverter?size=7&from=us" \
  -H "x-api-key: your_api_key_here"

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const res = await fetch('https://api.apiverve.com/v1/ringsizeconverter?size=7&from=us', {
  headers: { 'x-api-key': 'your_api_key_here' },
});

if (!res.ok) throw new Error(`${res.status} ${await res.text()}`);

const { data } = await res.json();
console.log(data);

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import requests

res = requests.get(
    "https://api.apiverve.com/v1/ringsizeconverter?size=7&from=us",
    headers={"x-api-key": "your_api_key_here"},
    timeout=15,
)
res.raise_for_status()

print(res.json()["data"])

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package main

import (
	"fmt"
	"io"
	"net/http"
)

func main() {
	req, _ := http.NewRequest("GET", "https://api.apiverve.com/v1/ringsizeconverter?size=7&from=us", nil)
	req.Header.Set("x-api-key", "your_api_key_here")

	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()

	out, _ := io.ReadAll(res.Body)
	fmt.Println(string(out))
}

Replace your_api_key_here with the key from your dashboard. When the inputs arrive as a list rather than one at a time, batch requests run up to 200 of them through this same API in a single call.

Authentication

Send your key in the x-api-key header. That is the only auth step — there is no token exchange and no per-endpoint scope to configure. Authentication covers creating, rotating and revoking keys.

Parameters

Sent in the query string. Premium parameters are accepted on every plan but only take effect on plans that include them.

Response

Every API returns the same three top-level keys, so one response handler covers your whole integration: status, error and data. Only data changes shape. Response format covers the envelope, the other output formats and how premium fields are withheld.

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{
  "status": "ok",
  "error": null,
  "data": {
    "input_diameter_mm": 17.3,
    "circumference_mm": 54.3,
    "conversions": {
      "diameter_mm": 17.3,
      "circumference_mm": 54.3,
      "us": 7,
      "uk": "N",
      "eu": 52,
      "jp": 17,
      "ch": -22,
      "au": "N"
    },
    "note": "Sizes are approximate. For accurate sizing, visit a jeweler."
  }
}

Response fields

Paths are relative to data. Premium fields are absent rather than zeroed on plans that do not include them, so check for presence instead of comparing to 0.

Errors

Read the HTTP status first, then error for the specific reason. The body names the parameter that has to change. Error handling covers the full status list and which of them are worth retrying.

Use cases

Jewelry E-commerce

Help customers find their ring size when purchasing from international jewelers and retailers

Gift Shopping

Convert ring sizes when buying jewelry gifts for people in different countries

Jewelry Sizing

Provide sizing tools for jewelers working with international customers and standards

Size Guides

Create comprehensive ring size conversion charts for jewelry product listings

Other ways to use Ring Size Converter

Set up Ring Size Converter on APIVerve, or reach the same source a different way. Your APIVerve account and credits work on all of them — one key, one balance.

Related

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