Bra size converter
A US 34C is a 75C in Europe, a 90C in France and a 12C in Australia. Type one size and see its label in all five systems, with cups after D matched by volume rather than by letter. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Size
- 34C
- System
- us
- Band index
- 3
- Cup index
- 3
- Systems
- us, uk, eu, fr, au
This bra size converter takes a band-and-cup size from one retail system and returns the matching labels in United States, United Kingdom, European, French, and Australian sizing. Shoppers who buy lingerie across borders constantly hit the same snag: a familiar thirty-four C in the US is not written the same way on a European rack, and cup letters after D diverge between UK double-letter ladders and EU single-letter steps. The conversion is fully deterministic: every supported size maps through a shared underbust band index and a shared cup volume index, then rebuilds the local label with fixed tables. There are no network calls, no brand vanity adjustments, and no date-dependent shortcuts.
What the bra size converter returns and which systems it understands
A bra size conversion answers a narrow question: given a band number and cup letter written in one country’s convention, what are the equivalent printed sizes in the other major markets. This calculator accepts a size string such as thirty-four C or seventy B and a system identifier, then returns structured blocks for US, UK, EU, French, and Australian systems plus a compact equivalents map of label strings.
Canonical systems are us for United States inch bands, uk for United Kingdom inch bands with the British cup ladder, eu for European centimetre-style bands, fr for French bands which sit fifteen units above the EU band, and au for Australian dress-style bra bands with a cup ladder that matches the UK.
Band ranges are even US and UK numbers from twenty-eight through fifty-two, EU bands from sixty through one hundred twenty in steps of five, French bands from seventy-five through one hundred thirty-five in steps of five, and even Australian bands from six through thirty. Cup letters after D are the part most people get wrong: the engine uses a shared volume index so US double-D aligns with UK double-D and EU E, while US triple-D aligns with UK E and EU F, and so on through higher cups.
How bands and cups are read and how results stay reproducible
Size parsing uppercases letters, strips spaces between the digits and the cup, and accepts common dual notations such as a slash form by taking the primary letter token. Optional leading zeros on the band are not required; ordinary integers in the system’s range are enough. Computation first locates the underbust index i from the band using fixed arithmetic: US and UK use twenty-eight plus two times i, EU uses sixty plus five times i, French uses seventy-five plus five times i, and Australian uses six plus two times i.
From the two indices the engine rebuilds every system’s band number and canonical cup letter, returning both structured objects and plain labels such as thirty-four C and seventy-five C.
Where multi-region bra sizes fit in shopping, retail, and software
International shoppers often hold a US or UK size from a home fitting and then open a European, French, or Australian product page that lists only local bands and cups, so a single deterministic converter prevents hand-table drift when comparing the same style across catalogs. Boutiques that import brands write purchase orders in the supplier’s system while tagging inventory for local customers; marketplaces normalize user-entered sizes before faceted search; customer support teams translate a return form size into the warehouse’s labeling convention in one step.
Teachers and textile courses assign homework that needs a fast, offline check of band and cup ladders without trusting opaque apps that silently change letter mappings. Developers call the same contract from scripts to seed deterministic test vectors for size-selector UIs, to normalize PDP attributes before cross-border shipping demos, or to satisfy programming-challenge statements that demand exact table lookups rather than a hand-waved rule of thumb.
Product tools use the conversion when a form offers a region toggle and must keep US double letters distinct from UK double letters and EU single letters after D. Pair it with general unit converters when you also need centimetres and inches for measuring tapes, and with catalog helpers when SKU attributes must stay consistent across locales.
What you can do with it
Cross-border lingerie shopping
Convert a known US or UK size into EU, French, and Australian labels before ordering from foreign product pages.
Retail catalog normalization
Map supplier size strings into local band and cup conventions for inventory tags, search facets, and returns.
FAQ
What does the bra size converter cost?
It is free in your browser on this page.
Why do cup letters differ after D?
UK and Australian charts use double-letter steps (DD, E, F, FF…), while EU and French charts use single letters (E, F, G…). The converter maps them through a shared volume index so US DD matches UK DD and EU E.
Does this tool recommend a size from body measurements?
No. It only converts an existing band-and-cup label between systems. It does not measure underbust or bust circumference or apply brand fit rules.
What is a US 34C in European sizes?
It is a 75C in European sizing, a 90C in French sizing and a 12C in Australian sizing, while the UK label stays 34C. You enter the size once and all five labels appear together.
Why is the French band number 15 higher than the European one?
French sizing counts its bands 15 units above the European ladder, so a European 75 becomes a French 90. The cup letter is matched separately, by volume, so it does not shift with the band.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/conv/bra-size \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"size":"34C","system":"us"}'const res = await fetch("https://api.kit.forhosting.com/conv/bra-size", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"size": "34C",
"system": "us"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/conv/bra-size",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"size": "34C",
"system": "us"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/bra-size", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"size":"34C","system":"us"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"size":"34C","system":"us"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/bra-size", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"size": "34C",
"system": "us"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "conv.bra_size",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Limits
max_band_index | 12 |
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
What the bra size converter returns and which systems it understands
Everyday aliases such as usa, gb, european, french, and australian normalize to those ids so forms, query strings, and spreadsheets can reuse the same contract without inventing private enums. There is no approximate feel-of-fit path and no sister-size expansion: the engine either maps both indices inside the supported ranges or rejects the input with invalid_input. Rejected cases include missing size or system, unparseable strings, unknown system names, band numbers outside the system’s ladder, and cup letters that are not on that system’s supported list.
How bands and cups are read and how results stay reproducible
The preferred fields are size for the band-plus-cup string and system for the source convention, with aliases value, label, bra_size, input_size, and s for the size, and from, region, sizing, country, source, and input_system for the system so heterogeneous clients can share one contract. The cup token is then looked up in that system’s alias table to a volume index, accepting US E as an alias for double-D and US F as an alias for triple-D so shoppers who learned either naming can enter either form. Pair the free browser run on this page with the priced API when you need the identical mathematical result inside an automated pipeline without re-implementing multi-region size charts yourself.
Where multi-region bra sizes fit in shopping, retail, and software
On this page the work runs entirely in your browser; through the API each successful lookup costs $0.002, failed validation is not charged, and nothing is stored after the response returns. That split — free interactive exploration and a priced, identical API — matches the rest of the KIT tier-A catalog and lets you move from a storefront demo to an automated pipeline without changing the mathematical result.
Integration use cases
Homework and CI fixtures
Generate reproducible multi-region bra size tables for worksheets, tutoring tools, and unit tests.
Technical questions
Which sizing systems are supported?
United States (us), United Kingdom (uk), European (eu), French (fr), and Australian (au), including aliases such as usa, gb, french, and australian.
What happens if I send an invalid band or cup?
The request fails with invalid_input and a message describing the expected band range or supported cup letters for that system. Invalid sizes are never silently mapped.