Hat Size Chart & Converter
Convert hat sizes between US, UK, and EU in real time. Enter your head circumference (cm or inch), or any hat size, and get every system instantly.
Step 1 — Measure
How to Measure Your Head for a Hat
Head circumference is the only measurement you need — every hat size system in this converter is derived directly from it.
- 1
Get a flexible tape measure
A soft cloth or vinyl tape measure works best. If you don't have one, a strip of string or paper works too — mark the overlap point, then measure that length against a ruler.
- 2
Position the tape correctly
Wrap the tape horizontally around your head, passing about 1/8 inch (1–2 cm) above your ears, across your forehead just above your eyebrows at the most prominent point, and around the widest, most protruding part of the back of your head.
- 3
Keep it snug, not tight
The tape should sit comfortably against your head without slipping — snug enough to hold its position, but not compressing your hair or skin. Take the reading in centimeters (or inches) directly from the tape.
- 4
Enter your measurement above
Type the circumference into the converter and select cm or inch. All three sizing systems — US, UK, and EU — appear instantly, along with the closest letter tier.
- 5
Round up if you're between two sizes
If your measurement falls between two rows in the chart, choose the larger size. A hat that's slightly loose can be adjusted with a sizing tape or sweatband insert; a hat that's too tight cannot be stretched safely on most materials.
Step 2 — Convert
Hat Size Converter
Input type
Unit
Wrap a tape measure around your head — see the HowTo steps on the left.
Enter a head circumference or hat size above to see the conversion.
Results update instantly as you type.
Hat Size Chart — All Systems
Scroll horizontally on mobile. Every row is a deterministic formula of head circumference — see the Editor's Notes below for the exact math.
| Head Circ. | US | UK | EU (cm) | Letter* |
|---|---|---|---|---|
| 50cm / 19⅝" | 6¼ | 6⅛ | 50 | XXS |
| 51cm / 20⅛" | 6⅜ | 6¼ | 51 | XXS |
| 52cm / 20½" | 6½ | 6⅜ | 52 | XS |
| 53cm / 20⅞" | 6⅝ | 6½ | 53 | XS |
| 54cm / 21¼" | 6¾ | 6⅝ | 54 | XS |
| 55cm / 21⅝" | 6⅞ | 6¾ | 55 | S |
| 56cm / 22" | 7 | 6⅞ | 56 | S |
| 57cm / 22½" | 7⅛ | 7 | 57 | M |
| 58cm / 22⅞" | 7¼ | 7⅛ | 58 | M |
| 59cm / 23¼" | 7⅜ | 7¼ | 59 | L |
| 60cm / 23⅝" | 7½ | 7⅜ | 60 | L |
| 61cm / 24" | 7⅝ | 7½ | 61 | L |
| 62cm / 24½" | 7¾ | 7⅝ | 62 | XL |
| 63cm / 24⅞" | 7⅞ | 7¾ | 63 | XL |
| 64cm / 25¼" | 8 | 7⅞ | 64 | XXL |
| 65cm / 25⅝" | 8⅛ | 8 | 65 | XXL |
* Letter tiers are a suggested midpoint — brand boundaries can shift by half a tier. Data cross-validated across 3 sources: sizeguide.net, Lock & Co (lockhatters.com), omnicalculator.com.
Editor's Notes: How We Picked These Numbers
Unlike ring, glove, or clothing sizing, hat sizes have no meaningful brand-to-brand disagreement on the core three systems — they're all deterministic functions of one physical measurement. Here's the exact math and the one place we did have to make a judgment call.
- EU size is simply your head circumference in centimeters, rounded — the most transparent hat sizing system in the world. A 56 cm head is an EU 56 hat, full stop, confirmed identically across all three sources we checked.
- US size is your head circumference in inches divided by π (≈3.14159), rounded to the nearest 1/8. For example: 56 cm = 22.05 inches ÷ π ≈ 7.02, which rounds to US 7 — exactly matching sizeguide.net's published table row for row.
- UK size is US size minus 1/8, confirmed by 3 independent sources (sizeguide.net, Lock & Co, and cross-referenced against omnicalculator's US/UK pairs). We found one outlier — size.ly's chart lists UK as equal to US with no offset — but since every other source we checked (including a 349-year-old hat maker) agrees on the 1/8 offset, we treated size.ly's version as a data-entry inconsistency and did not use it.
- S/M/L/XL letter tiers are the one place brands genuinely disagree — omnicalculator and size.ly draw the boundary between adjacent tiers about half a size apart. Rather than pick a winner, we chose a midpoint (S≈55–56cm, M≈57–58cm, L≈59–61cm, XL≈62–63cm) and flag every letter result with a note pointing back to the exact cm measurement, which is unambiguous.
- We did not include French or Japanese/Korean hat sizing as separate columns. The one specialized source we found for a French scale (rosenlake.net) was unreachable during our research (TLS certificate error), and JP/KR hat retailers overwhelmingly sell by EU (cm) sizing directly with no separate scale — so cm is already the correct answer for those markets.
Understanding Hat Size: The Physical Basis
A hat size describes the circumference of the widest part of your head — the point the hat band actually rests on. Unlike shoe or ring sizing, where multiple regional standards evolved independently and sometimes conflict, hat sizing is unusually clean: every major system (US, UK, EU) is a direct mathematical transformation of the same physical number, head circumference.
The EU system is the most literal: your EU hat size is your head circumference in centimeters, rounded to the nearest whole number. A 58 cm head wears an EU 58 hat. The US system converts that same circumference to inches and divides by π (approximately 3.14159), because a US hat size traditionally described the diameter of the head opening rather than its circumference — and circumference = π × diameter, so dividing by π recovers that diameter-like number. US sizes are expressed in eighths (7, 7⅛, 7¼, and so on) because that was the precision hatters historically worked to when blocking felt over a wooden head form. The UK system is simply the US number minus 1/8 — a historical offset from when British and American hatters used slightly different reference blocks, which has stuck as a fixed 1/8-inch difference ever since.
Because all three numbers derive from one measurement, you never actually need three separate charts memorized — if you know your head circumference in centimeters, you can compute all three sizes yourself: EU = round(cm); US = (cm ÷ 2.54 ÷ π), rounded to the nearest eighth; UK = US − ⅛. This converter does exactly that arithmetic, plus a nearest-row lookup against a verified chart so you also get a sanity-checked letter tier.
Letter tiers (XS/S/M/L/XL/XXL) are the softest part of hat sizing. They exist because many mass-market and fast-fashion hats — beanies, baseball caps, bucket hats — are manufactured with stretch panels or adjustable straps rather than a fixed-size felt block, so brands sell them by loose tier rather than precise numeric size. Because there's no governing standard for where one tier ends and the next begins, the same head circumference can be labeled 'M' by one brand and 'L' by another. If a product only lists a letter size, look for the brand's own cm range in fine print before you buy; if it lists a numeric US/UK/EU size, that number is unambiguous and this converter's results will match it directly.
Children's hat sizing follows the same cm-circumference logic but is typically sold by age bracket (0–6 months, 6–12 months, 1–2 years, and so on) rather than a numeric scale, because head growth in early childhood is rapid and age is a more practical shopping filter than a precise circumference number for most buyers. This converter focuses on adult sizing, where the numeric systems are well established and stable.
Data Sources & Standards
Hat size data is the cleanest in our size-converter family: all three systems are exact formulas of head circumference, cross-checked against 3 independent sources with no unresolved conflicts (the only discrepancy found — size.ly listing UK = US — was an isolated outlier and was not used).
No data is stored. All calculations run locally in your browser.
Frequently Asked Questions
- How do I measure my head for a hat size?
- Wrap a soft tape measure horizontally around your head, passing about 1/8 inch (1–2 cm) above your ears, across your forehead just above the eyebrows, and around the most prominent point at the back of your head. Keep the tape snug but not tight, and read the measurement in cm or inches. Enter that number into the converter above to see your US, UK, and EU size instantly. If you don't have a tape measure, a strip of string or paper works — mark where it overlaps, then measure that length against a ruler.
- What is the hat size chart for cm to inches?
- Head circumference in cm converts to inches by dividing by 2.54 (or multiplying by 0.3937). For example, 56 cm ÷ 2.54 = 22.05 inches, and 58 cm ÷ 2.54 = 22.83 inches. The full chart in this converter (50–65 cm) lists both units side by side for every row, alongside the matching US, UK, and EU hat sizes — no manual math required.
- How does US hat size convert to UK hat size?
- UK hat size is exactly US hat size minus 1/8 (confirmed across 3 independent sources, including 349-year-old British hatter Lock & Co). For example, US 7 = UK 6⅞, and US 7½ = UK 7⅜. This fixed 1/8-inch offset comes from historical differences in the wooden head blocks American and British hatters used, and it applies consistently across the whole sizing range.
- How do I convert EU hat size to US?
- EU hat size is your head circumference in centimeters, rounded — so to get US size, first convert that cm figure to inches (divide by 2.54), then divide by π (≈3.14159) and round to the nearest eighth. For example, EU 56 → 56 cm ÷ 2.54 = 22.05 in ÷ π ≈ 7.02, which rounds to US 7. Enter your EU size directly into the converter above and it performs this calculation automatically.
- What size is a medium hat in cm?
- There's no single official cutoff, since letter tiers vary by brand — but a common midpoint used across major sizing charts puts 'Medium' at roughly 57–58 cm head circumference (US 7⅛–7¼, UK 7–7⅛). If a hat only lists a letter size, check the brand's own cm range before buying, since one brand's 'M' can be another's 'S' or 'L'. For a guaranteed fit, always prefer a hat listed by numeric size (US/UK/EU) or exact cm range over a letter tier alone.
- How to measure hat size without a tape measure?
- Cut a length of string or a strip of paper and wrap it around your head following the same path as a tape measure — about 1/8 inch above the ears, across the forehead above the eyebrows, and around the back of the head at its widest point. Mark the point where it overlaps itself, then lay the string or paper flat and measure that length against a ruler in cm or inches. Enter the result into the converter above for your full size chart.
- Do I round up or down if I'm between two hat sizes?
- Round up. A hat that's slightly larger than your exact measurement can usually be tightened with an internal sizing tape, sweatband insert, or adjustable strap (on caps and beanies with one). A hat that's too small generally cannot be safely stretched, especially structured felt or straw hats, and wearing one that's too tight for long periods can cause headaches. This converter snaps your input to the nearest half-size row and flags when that snapping occurred.
- Are hat sizes the same for men and women?
- The US/UK/EU numeric sizing systems in this converter are unisex — they describe head circumference directly, regardless of gender, and apply the same way to any adult head. Some brands market separate 'men's' and 'women's' hat collections, but that distinction is typically about style and silhouette (crown height, brim shape), not a different sizing formula. If a product lists a numeric or cm size, use this converter's chart directly; if it only lists a gendered letter tier, check the brand's specific cm range.
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