Hat size converter
A US 7 fitted hat is a UK 6 7/8, a European 56 and a head of 56 cm, about 22.05 inches. Enter the size you know in any of those systems and see the others in one row before you order. Free in your browser.
- Free
- Runs in your browser
- No sign-up
- Your data stays on your device
Run — free
Worked example
- Size
- 7
- Input scale of 'size'
- us
- Input size
- 7
- Input scale
- us
- Us
- 7
- Us num
- 7
Hat size converter tools exist because fitted caps, fedoras, berets, and hard hats are sold under incompatible label systems across continents. A shopper in Chicago sees a US seven, a London milliner marks the same crown with a British six and seven eighths, a continental catalogue prints a European fifty-six, and a soft tape around the head reports about fifty-six centimetres or twenty-two inches. Ordering the wrong scale means returns, restocking fees, and a bad first impression for gift buyers.
How US, UK, EU and circumference hat sizes relate
Physical fit for a fitted hat is governed by the circumference of the head just above the ears and eyebrows, where the sweatband sits. The US fitted scale is a numeric sequence that rises in one-eighth steps for most adult catalogue ranges from about six and one half to eight; each step corresponds to a fixed increment of circumference on standard millinery charts.
The UK scale uses the same fractional style but is typically one eighth smaller than the matching US label for the same head, which is why a US seven lines up with a UK six and seven eighths on common charts. The EU or continental centimetre size that shoppers meet on European packaging is usually the head circumference in centimetres rounded to a whole number, so a European fifty-six is in the same family as a tape reading of fifty-six centimetres.
Measuring with a soft tape, a printable sizer, or a known well-fitting hat ultimately produces centimetres or inches of circumference; converting that measurement into a labelled size is a table lookup, not a fashion claim. This tool stores a fixed industry-aligned table of known combinations and derives inches as centimetres divided by two point five four so geometry stays consistent. It does not interpolate unofficial intermediate sizes, claim medical fit for swollen temples, convert clothing or ring sizes, or call external product databases.
It answers the conversion intent people mean when they search for a hat size converter and expect US, UK, EU centimetre, and circumference columns side by side for one known input.
Where hat size conversion shows up in real work
Online hat and cap retailers and marketplace sellers list inventory with mixed US and EU tags and need one ground-truth row before shipping internationally so returns from wrong-scale orders fall. Corporate uniform and promotional product teams map a measured head circumference from an employee form into US and UK labels for vendor portals that still require fitted fractions. Event merchandising and sports team shops help fans translate a UK fraction from a high-street sizer into a US web checkout without walking them through a spreadsheet.
Manufacturing and CAD teams store head circumference in centimetres while marketing copy must print local labels, and a single conversion call keeps both systems honest. Customer support bots that answer “what is a US seven and one quarter in EU?” can invoke this capability instead of hard-coding brittle charts that drift between documents.
If you later need ring size conversion, shoe size charts, general length unit conversion, or product search against a live catalogue, treat those as separate search intents and landings rather than overloading this hat size converter page.
What you can do with it
Cross-border hat and cap checkout
Map a customer’s US or UK fitted size to EU centimetre and circumference labels before international shipping so the crown that leaves the warehouse matches the head that ordered it.
Tape measure to catalogue labels
Convert a measured head circumference in centimetres or inches into US, UK, and EU labels for product pages, gift guides, and packaging.
FAQ
Which hat size systems does this converter support?
US fitted fractions (6 1/2–8 in eighth steps), UK fitted fractions (6 3/8–7 7/8), EU centimetre sizes (52–64), and head circumference in centimetres or inches. Inches are derived as cm / 2.54.
What happens if I enter an out-of-range size?
The table does not invent intermediate sizes; only known chart rows are returned so catalogue labels stay honest.
How precise is circumference matching?
Centimetre inputs match a table row within about ±0.35 cm and inch inputs within about ±0.14 in so common rounded tape readings still resolve. US and UK inputs require an exact fitted table value.
Does this measure my head?
No. You must already know a size or circumference. Measuring a head is a physical step; this capability only converts known labels among the supported scales.
What hat size fits a 57 cm head?
A head of 57 cm matches a US fitted 7 1/8. The European label follows the circumference in whole centimetres, so it reads 57 as well.
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/hat-size \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"size":"7","scale":"us"}'const res = await fetch("https://api.kit.forhosting.com/conv/hat-size", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"size": "7",
"scale": "us"
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/conv/hat-size",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"size": "7",
"scale": "us"
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/conv/hat-size", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"size":"7","scale":"us"}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"size":"7","scale":"us"}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/conv/hat-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": "7",
"scale": "us"
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "conv.hat_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.
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
This capability accepts one known size plus its scale, looks it up in a fixed deterministic conversion table covering common adult US fitted sizes from six and one half through eight with matching UK fractions, EU centimetre labels, and head circumference in centimetres and inches, and returns every equivalent in one JSON row. Out-of-range or unknown sizes fail with a clear invalid_input error instead of inventing a near match that would mis-fit.
What you send and what you get back
Send two fields: size and scale. Size is the value you already know: a fitted fraction or decimal such as seven or seven one eighth for US and UK scales, a centimetre number such as fifty-six for EU or head circumference in centimetres, or an inch circumference such as twenty-two point zero five for the inches scale. Optional alternate keys value or hat for the size and system, from, or unit for the scale are accepted for convenience. Classic checks include US seven mapping to UK six seven eighths, EU fifty-six, and about twenty-two point zero five inches; centimetre fifty-seven mapping to US seven one eighth; and an out-of-range US ninety-nine failing cleanly. Scale names the system of that value and accepts us, uk, eu, cm, and in, with aliases including usa, british, europe, circumference, head, and inches. Missing fields, empty strings, non-finite numbers on numeric scales, and completely unknown or out-of-range combinations fail with invalid_input and are not charged; the error message points at supported ranges so clients can correct the label rather than guess. On success the response echoes input_size and input_scale, returns us and uk as canonical fraction strings plus us_num and uk_num, eu, circumference_cm, and circumference_in with stable twelve-significant-digit cleaning, nests the same values under scales, and includes method table_lookup plus a short formula string. Pricing for successful API calls is the published base of $0.002 per item; validation failures do not consume prepaid balance.
Where hat size conversion shows up in real work
Data pipelines cleaning product feeds with fields like size_us, uk_size, and head_cm can normalise every SKU through the same table and reject unknown codes early. Because this capability is a pure parse engine, API pricing is the published base of $0.002 per successful item and failed validation does not consume balance.
Integration use cases
Support macros and chatbots
Answer “what is a size 7 in UK and EU?” with one deterministic JSON row instead of copy-pasting from a PDF chart.
Technical questions
Is the browser tool free?
Yes. The tier-A browser widget runs locally at no charge. API requests use prepaid KIT balance at $0.002 per successful item; invalid input is not charged.