How do I measure my head?

Use a soft fabric measuring tape (or string + ruler). Wrap around head at widest point — mid-forehead, just above ears, around back of skull. Snug but not tight. Measure in cm. Round up to nearest 0.5 cm. Most adult heads measure 54-62 cm; women average 55-57, men 57-59.

What if I'm between sizes?

Size up. Hats slightly too large can be adjusted with a sweatband insert ($5-10) or hat-size-reducer foam strip. Hats too small can't be stretched meaningfully — fitted caps in particular are unforgiving. Cowboy hats can be steamed for slight stretch but it's a hat-shop service, not DIY.

Round vs oval head shape?

Most heads are oval (longer front-to-back than side-to-side). Most hats are designed for oval. Some people have round heads (equal dimensions); those need round-shaped hats or experience side-pressure pain in oval hats. Hat shops can identify your shape with a conformator. For most online shoppers, assume oval and pick standard hats.

Slightly. Fitted caps stretch about 0.25-0.5 size after consistent wear. Cowboy hats stretch about 0.5 size with steam-and-wear. Knit / fabric hats stretch 1+ size. Don't buy too small expecting major stretch — fitted caps especially won't accommodate more than tiny growth.

Why do brands fit differently?

Different head-shape assumptions and band materials. New Era fits standard oval. Stetson Royal cowboy assumes long-oval shape. Patagonia/Carhartt run slightly large. European brands (Borsalino, Christys') often fit smaller than US brands at same labeled size. Always check brand's size chart in cm; trust measurement over labels.

Do hat sweatbands matter?

Yes for comfort and fit. Quality leather sweatbands (cowboy hats, dress hats) absorb sweat without ruining shape. Cheap synthetic bands deteriorate fast. Budget hats often skip sweatbands entirely. For frequent-wear hats, sweatband quality affects lifespan and comfort more than crown material does.

File & Format Converters · Free tool

Hat Size Converter

Convert your hat size between US, UK, and EU formats using head circumference in centimeters. Find your perfect fit instantly with this free, no-sign-up online tool.

Updated June 2026

Input typeHead circumference (cm)

6 7/8

EU (cm)

Letter

How to measure your head

Use a soft tape (or wrap a string and measure on a ruler). Place it about 1 cm above your ears and just above your brow — where a hat normally sits. Hold it level and snug, not tight. Measure twice and take the larger of the two.

US	UK	EU (cm)	Letter
6 1/2	6 3/8	52	XS
6 5/8	6 1/2	53	XS
6 3/4	6 5/8	54	S
6 7/8	6 3/4	55	S
7	6 7/8	56	M
7 1/8	7	57	M
7 1/4	7 1/8	58	L
7 3/8	7 1/4	59	XL
7 1/2	7 3/8	60	XL
7 5/8	7 1/2	61	XXL
7 3/4	7 5/8	62	XXL
7 7/8	7 3/4	63	3XL
8	7 7/8	64	3XL

Between sizes? Wool felt hats stretch up to ~1 cm — size down. Straw hats don’t stretch — size up. Fitted caps (New Era 59FIFTY etc.) run true to US fractional sizes.

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What it does

Hat sizing uses four parallel systems worldwide. US sizing is fractional inches based on inner-band diameter (sizes 6 5/8 to 8, common range 7 to 7 5/8). UK sizing is similar but offset (US 7 = UK 6 7/8). European sizing uses centimeter circumference directly (54-64 cm). Generic alpha sizing (S/M/L/XL/XXL) varies wildly by brand. The underlying physical measurement is head circumference at widest point — typically mid-forehead, just above ears, around back of head. US 7 = UK 6 7/8 = EU 56 cm = Medium (most brands). Measuring once gives you the truth that translates across systems.

The converter takes any size in any system OR head circumference in cm/inches, then returns equivalents across all four. String- and-ruler home measurement: take a string (or fabric tape), wrap around your head at widest point (mid-forehead through back of skull), mark where it overlaps, measure the string in cm. Round up to nearest 0.5 cm. Cross-reference with brand-specific sizing charts before ordering. Cowboy hats, fitted baseball caps, and dress hats are typically most precise; structured fashion hats and casual snap-backs have more give.

Brand-specific quirks worth knowing: New Era fitted MLB caps run true-to-size if you measure correctly. Stetson and Resistol (cowboy hats) require precise sizing; they don't stretch or shrink much. Patagonia and Carhartt typically run slightly large; size down half. Brixton fashion hats run true. For high-stakes fits (custom hats, expensive cowboy hats), have a hat shop measure professionally — they can identify oval vs round head shape (different brands favor different shapes).

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How to use it

Measure head circumference at widest point with string + ruler, OR enter a known size.
Pick source system: US / UK / EU / cm / alpha.
Read all equivalents.
Cross-check with the specific brand's size chart.
For expensive hats, get measured at a hat shop.

When to use this tool

Online ordering hats from international brands or retailers.
Buying a fitted baseball cap (New Era, etc.) where exact size matters.
Cowboy / dress hat purchase where fit is critical and brand-specific.
Cross-shopping multiple hat retailers with different size systems.
Gift purchasing — converting from someone's known size in their country.

When not to use it

Adjustable / snap-back caps — one-size-fits-most, no precise sizing needed.
Stretchy beanies / knit hats — flex enough that exact size rarely matters.
Costume / Halloween hats — those run loose / generic.
Children's hats — different age-based sizing.

Common use cases

Verifying a number or output before passing it on
Quick conversion during a typical workday
Pre-decision sanity-check on inputs and outputs
Educational use — demonstrating the underlying concept

Frequently asked questions

How do I measure my head?: Use a soft fabric measuring tape (or string + ruler). Wrap around head at widest point — mid-forehead, just above ears, around back of skull. Snug but not tight. Measure in cm. Round up to nearest 0.5 cm. Most adult heads measure 54-62 cm; women average 55-57, men 57-59.
What if I'm between sizes?: Size up. Hats slightly too large can be adjusted with a sweatband insert ($5-10) or hat-size-reducer foam strip. Hats too small can't be stretched meaningfully — fitted caps in particular are unforgiving. Cowboy hats can be steamed for slight stretch but it's a hat-shop service, not DIY.
Round vs oval head shape?: Most heads are oval (longer front-to-back than side-to-side). Most hats are designed for oval. Some people have round heads (equal dimensions); those need round-shaped hats or experience side-pressure pain in oval hats. Hat shops can identify your shape with a conformator. For most online shoppers, assume oval and pick standard hats.
Will hats stretch?: Slightly. Fitted caps stretch about 0.25-0.5 size after consistent wear. Cowboy hats stretch about 0.5 size with steam-and-wear. Knit / fabric hats stretch 1+ size. Don't buy too small expecting major stretch — fitted caps especially won't accommodate more than tiny growth.
Why do brands fit differently?: Different head-shape assumptions and band materials. New Era fits standard oval. Stetson Royal cowboy assumes long-oval shape. Patagonia/Carhartt run slightly large. European brands (Borsalino, Christys') often fit smaller than US brands at same labeled size. Always check brand's size chart in cm; trust measurement over labels.
Do hat sweatbands matter?: Yes for comfort and fit. Quality leather sweatbands (cowboy hats, dress hats) absorb sweat without ruining shape. Cheap synthetic bands deteriorate fast. Budget hats often skip sweatbands entirely. For frequent-wear hats, sweatband quality affects lifespan and comfort more than crown material does.

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