Free hat size calculator
Find your hat size in two seconds. Enter your head circumference in centimetres or inches and the hat size calculator returns your US, UK, and European (metric) sizes plus the S/M/L letter size — with a full hat size chart and how to measure your head, updated live, as you type.
On this page15 sections
| cm | US | UK | Letter |
|---|---|---|---|
| 52 | 6½ | 6⅜ | XS |
| 53 | 6⅝ | 6½ | XS |
| 54 | 6¾ | 6⅝ | S |
| 55 | 6⅞ | 6¾ | S |
| 56 | 7 | 6⅞ | M |
| 57 | 7⅛ | 7 | M |
| 58 | 7¼ | 7⅛ | L |
| 59 | 7⅜ | 7¼ | L |
| 60 | 7½ | 7⅜ | XL |
| 61 | 7⅝ | 7½ | XL |
| 62 | 7¾ | 7⅝ | XXL |
| 63 | 7⅞ | 7¾ | XXL |
| 64 | 8 | 7⅞ | XXXL |
A starting size from the standard fitted-hat formula, not a brand fit. If between sizes, size up
Results are estimates. Consult a professional.
What is a hat size?
Your hat size is a number that describes how big around your head is — and therefore which hat will sit comfortably on it. Every system starts from the same measurement: the circumference of your head, the distance all the way around it just above your ears and eyebrows. This hat size calculator takes that one measurement and returns your size in all four common systems at once: US, UK, European (metric), and the simple S/M/L/XL letter sizing.
The reason a calculator helps is that the systems do not look alike. A single 58 cm head is a European size 58, a US 7¼, a UK 7⅛, and a Large — four different-looking labels for exactly the same hat. Knowing all four means you can buy with confidence whether the tag is metric, fractional, or just a letter.
How the hat size calculator works
Fitted hat sizes are not arbitrary — they are geometric. A hat opening is roughly a circle, so a head of a given circumference needs an opening of a matching diameter. Because circumference = π × diameter, you get the US (and UK) fitted size by dividing the head circumference in inches by π (about 3.14159):
A quick worked figure: a 22-inch head gives 22 ÷ π = 7.00, which rounds to a US size 7. The UK equivalent is one eighth smaller (6⅞), and in centimetres 22 inches is about 56 cm, so the European size is 56. The calculator runs this on every value you type and shows all four systems side by side.
How to measure your head for a hat
The whole result depends on one accurate measurement, and it takes about ten seconds with a soft tape measure. Measure around the largest part of your head — not at an angle, and not too tight.
- Wrap a soft tape measure around your head about one finger-width (roughly 1 cm / ½ inch) above your ears and eyebrows — the fullest part of your head.
- Keep the tape level all the way around, horizontal front to back, snug against your head but not squeezing.
- Read the circumference where the tape meets, in centimetres or inches. Take the measurement two or three times and use the largest reading.
- No tape measure? Wrap a piece of string or a strip of paper around your head, mark where it overlaps, then lay it flat against a ruler.
A worked example using the hat size calculator
Daniel measures his head and gets 58 cm (about 22.8 inches). He wants to know his size before buying a hat online that lists US, UK, and European labels. Here is exactly how the calculator gets there.
Step 1 — Enter the head circumference
He sets the unit to centimetres and enters 58. The European (metric) size is read off directly — in the EU system the size simply is the circumference in centimetres, so 58 cm is a European size 58.
Step 2 — Convert to the US fitted size
58 cm is 22.83 inches. Divide by π: 22.83 ÷ 3.14159 = 7.27, which rounds to the nearest eighth as 7¼. That is Daniel's US fitted hat size.
Step 3 — Read the UK size and letter size
The UK size is one eighth smaller than the US size, so 7¼ becomes 7⅛. A 58 cm head also falls in the Large band of S/M/L/XL sizing. The calculator shows all four at once.
| System | Daniel's size |
|---|---|
| Head circumference | 58 cm (22.8 in) |
| US fitted size | 7¼ |
| UK fitted size | 7⅛ |
| EU / metric size | 58 |
| Letter size | L (Large) |
One 58 cm head, shown in all four sizing systems — exactly what the calculator returns.
Hat size chart: cm to US, UK, EU and letter sizes
This chart converts head circumference (in centimetres and inches) to a US fitted size, a UK fitted size, the European metric size, and the S/M/L/XL letter size. It covers the everyday adult range, 52 to 64 cm. Find your measured circumference in the first column and read across.
| Head (cm) | Head (in) | US size | UK size | EU size | Letter |
|---|---|---|---|---|---|
| 52 | 20.5 | 6½ | 6⅜ | 52 | XS |
| 53 | 20.9 | 6⅝ | 6½ | 53 | XS |
| 54 | 21.3 | 6¾ | 6⅝ | 54 | S |
| 55 | 21.7 | 6⅞ | 6¾ | 55 | S |
| 56 | 22.0 | 7 | 6⅞ | 56 | M |
| 57 | 22.4 | 7⅛ | 7 | 57 | M |
| 58 | 22.8 | 7¼ | 7⅛ | 58 | L |
| 59 | 23.2 | 7⅜ | 7¼ | 59 | L |
| 60 | 23.6 | 7½ | 7⅜ | 60 | XL |
| 61 | 24.0 | 7⅝ | 7½ | 61 | XL |
| 62 | 24.4 | 7¾ | 7⅝ | 62 | XXL |
| 63 | 24.8 | 7⅞ | 7¾ | 63 | XXL |
| 64 | 25.2 | 8 | 7⅞ | 64 | XXXL |
US size = circumference ÷ π rounded to the nearest 1/8; UK = US − 1/8; EU = circumference in cm. Every row is computed by the same engine as the calculator above.
What is the average hat size?
Most adult heads fall in a fairly narrow band. The average men's hat size is about 7⅛ to 7⅜ in the US system — a 57 to 59 cm head, usually a Medium to Large. The average women's hat size is roughly 6⅞ to 7⅛, a 55 to 57 cm head, usually a Small to Medium.
| Group | Typical circumference | US size | Letter |
|---|---|---|---|
| Average woman | 55–57 cm | 6⅞ – 7⅛ | S–M |
| Average man | 57–59 cm | 7⅛ – 7⅜ | M–L |
| Child (over ~5 yrs) | 51–53 cm | 6⅜ – 6⅝ | XS |
Typical adult and older-child ranges. Individual heads vary widely — always measure rather than assume.
Fitted hats vs adjustable hats
How precisely you need to know your size depends on the hat. Fitted hats — structured caps, felt hats, Panama hats, and most quality headwear — come in specific sizes (7, 7⅛, 7¼ …) and only fit one head size, so the calculator's exact number matters. Adjustable hats use a strap, snapback, or elastic and stretch across a range of sizes, so the letter size or even "one size fits most" is usually enough.
- Fitted — buy your exact US/UK/EU size; if between sizes, go up and use sizing tape.
- Snapback / strapback — adjustable at the back; one size covers roughly 55–62 cm.
- Flexfit / stretch-fit — sold in S/M and L/XL letter bands that flex around a couple of sizes.
- One size fits most — typically fits about 56–60 cm; check the stated range if your head is small or large.
US vs UK hat sizing (the one-eighth difference)
US and UK fitted hats use the same-looking fractional scale, which causes confusion — but they are not identical. For the same head, a UK size runs one eighth of an inch smaller than the US size. So a head that is a US 7¼ is a UK 7⅛; a US 7 is a UK 6⅞.
The European (metric) system sidesteps the issue entirely by labelling hats with the head circumference in centimetres, so there is nothing to convert — a 58 cm head is a size 58 hat. When you buy across regions, match on the metric size if it is given, or apply the one-eighth shift between US and UK.
Tips for a hat that fits
- Measure, don't guess. Heads vary far more than people expect; a ten-second tape measurement beats assuming you are an average size.
- When between sizes, size up. A larger hat is easily made to fit with foam sizing tape or an inner band; a small one cannot be stretched comfortably.
- Account for hair. If you usually wear your hair up or have thick hair, measure as you will wear the hat, or add a few millimetres.
- Check the brand's own chart. There is no universal standard, so confirm the size against the specific maker's chart, especially for felt and straw hats.
- A good fit is snug, not tight. The hat should rest on your head without leaving a red mark or sliding off when you look down.
For other sizing conversions, pair this with the shoe size calculator or the bra size calculator.
How this calculator works and sources
This hat size calculator applies the standard fitted-hat geometry: the US size equals the head circumference in inches divided by π, rounded to the nearest eighth; the UK size is one eighth smaller; the European size is the circumference in centimetres; and the letter size is a band of that circumference. The maths runs entirely in your browser — your measurement is never sent anywhere. The conversions and how-to-measure guidance follow the sizing charts published by established hatters.
Lock & Co. Hatters — Hat Size Chart & How to Measure Your Hat Size.Tilley — Hat Sizing Guide.Frequently asked questions about the free hat size calculator
About this hat size calculator
This hat size calculator runs entirely in your browser. The head circumference you enter never leaves your device — nothing is sent to a server, logged, or shared. It applies the standard fitted-hat formula (US size = circumference in inches ÷ π, rounded to the nearest eighth; UK = US − 1/8; EU = circumference in cm) and updates instantly on every change.
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